CONTROL OF THE SENATE, the big prize in tomorrow's election package, will hinge on the Democrats' ability to make a net gain of at least the four seats needed to overturn the 53-47 Republican margin in the last Congress. The race is expected to be close, in part because the Republicans will have 22 seats up for grabs Tuesday; the Democrats, only 12.

If President Reagan's exertions on behalf of individual GOP candidates help hold the Senate for the Republicans, there would be relatively little change in the Washington power structure.A Democratic gain of more than the net three seats that would produce a 50-50 tie to be broken for the Republicans by the vice president would alter those power relationships significantly.

The ability of the Senate Republican leadership to continue to play the difficult role of broker between the White House and the House, where the Democrats seem certain to retain control, would be greatly diminished. The last two years of the Reagan presidency probably would be marked by much more partisanship than otherwise.

In the Senate itself, Democratic control would turn over all committees and their chairmanships to that party. Here is a look at the likely impact of Democratic majorities and the new chairmen on key Senate committees and subcommittees:

APPROPRIATIONS - The chairmanship is expected to pass from Sen. Mark O. Hatfield, R-Ore., to Sen. John C. Stennis, D-Miss. Staffers feel the committee is less partisan than most other committees. Democratic control thus would make comparatively little difference, although a changing of the guard would

put a different tilt on things. Sen. Stennis is considered more of a conservative by temperment than Sen. Hatfield, particularly in the area of defense. But much of the committee's power has eroded in recent years as Congress and the Reagan administration have chosen to fund the government through omnibus continuing resolutions rather than through the normal appropriations bill process. Chairmanship of the transportation appropriations subcommittee likely would go to Sen. Lawton Chiles, D-Fla. The current chairman, Sen. Mark Andrews, R-N.D., has had confrontations with the Interstate Commerce Commission.

BANKING, HOUSING AND URBAN AFFAIRS - Former chairman William Proxmire, D-Wis. would replace Sen. Jake Garn, R-Utah, as chairman. Sen. Proxmire is likely to insist that the price of any banking legislation is closing the non-bank bank loophole through which non-banking firms are conducting banking business beyond the reach of federal banking laws.

Sen. Proxmire made it clear this year that he cannot be stampeded into enacting legislation that bank regulators say they need to allow for interstate mergers of failing institutions since he is not convinced it is really necessary.

He does favor providing some limited securities powers to banks and may be more receptive to pressure from Sen. Christopher Dodd, D-Conn., to close the South Dakota loophole through which state banks affiliated with national bank holding companies could start marketing insurance nationwide.

Sen. Proxmire is not expected to veer from his past course of approving U.S. participation in World Bank and International Monetary Fund aid and his support of Export-Import Bank programs.

BUDGET - The impact of the change on this committee could mirror that on the Senate as a whole. Chairman Pete Domenici, R-N.M., working with other Senate GOP leaders and with the senior Democrat most likely to replace him, Sen. Lawton Chiles, Fla., has played a major role in arranging budget compromises acceptable to both the White House and the Democratic House. The Domenici- Chiles cooperation probably would continue but even the limited budget compromises of recent years will be more difficult to reach. The Gramm-Rudman deficit reduction act will require an even larger cut in the deficit next year and that will confront the committee with such questions as the level of defense and entitlement program spending and a tax increase. Those issues already divide the president and the House; they could become much more divisive in a partisan battle between Mr. Reagan and a Congress completely controlled by the Democrats.

COMMERCE, SCIENCE AND TRANSPORTATION - Sen. Ernest Hollings, D-N.C., who is in line to take over the committee shares the skepticism of the current chairman, Sen. John Danforth, R-Mo., about the need for major changes in truck and rail regulatory laws. A return to the days of stringent entry controls is not expected under a Hollings chairmanship but deregulation legislation would not sail through.

Sen. Hollings is expected to put more emphasis on maritime issues, reflecting the port interests in his home state. He would be certain to do all he can to head off product liability legislation sought by the insurance industry; he and Sen. Danforth were on opposite sides of the last-minute effort to bring such legislation to the Senate floor this year. A switch to Democratic control also would mean that Sen. Robert Packwood, R-Ore., would lose the chairmanship of the Surface Transportation Subcommittee that he has used as a forum for deregulation legislation.

ENERGY AND NATURAL RESOURCES - The chairmanship of the committee would shift

from Sen. James McClure, R-Idaho, to Sen. J. Bennett Johnston, D-La., unless Sen. Johnston is successful in his bid for Majority Leader. In that case, chairmanship of the committee would be transferred to Sen. Dale Bumpers, D- Ark. Sen. Johnston is a strong advocate of the oil and gas industry. He supports a strong strategic petroleum reserve program and spoke in favor of oil and gas industry promotional legislation that was pending in the Senate as Congress adjourned this year. Owing to the interests of New Orleans area terminals, he also is a strong supporter of U.S. coal exports, having backed port and inland waterway improvement legislation and coal slurry pipeline bills. Sen. Bumpers is considered a consumer advocate and conservationist. He has supported legislation to make oil and gas leasing more competitive and favors repealing the Fuel Use Act. A changeover also would make Sen. Wendell Ford, D-Ky., chairman of the energy research subcommittee, if he is re- elected, and Sen. John Melcher, D-Mont., chairman of the natural resources subcommittee.

ENVIRONMENT AND PUBLIC WORKS - Sen. Quentin Burdick, D-N.D., is the most likely candidate to succeed Sen. Robert Stafford, R-Vt., as chairman. The Democratic leadership would tackle interstate highway funding legislation and related issues - billboards and the 55 mph speed limit. It probably would be harder for the Reagan administration to push for major changes in the highway funding procedures, which the next Congress must deal with. The Democrats also would take up clean water legislation if the bill passed by Congress is vetoed by President Reagan. The acid rain issue would be addressed and a new ground water bill is expected to surface. Sen. George Mitchell, D-Maine, considered a strong environmentalist, would be in line for a subcommittee chairmanship.

FINANCE - Sen. Packwood, is expected to be replaced as chairman by Sen. Lloyd Bentsen, D-Texas. The shift would bring the Senate more into line with the House on the issue of a tax increase. The House Ways and Means chairman, Dan Rostenkowski, D-Ill., has been speaking out in favor of such a deficit- reducing step and Sen. Bentsen could join him. The two predictably would part ways over the composition of the increase. Sen. Bentsen has agitated long and hard for an oil import fee, and would likely make it a high priority but Rep. Rostenkowski would oppose such a measure.

Sen. Bentsen also may take over the chairmanship of the International Trade Subcommittee. He has sponsored tough trade bills labeled by the Reagan administration as protectionist. At the end of the last Congress, he and other key committee members agreed to a toned-down, compromise trade bill. The committee did not act on it and Sen. Bentsen is likely to be among those who press for a second try next year.

If Sen. Bentsen leaves open the trade subcommittee job, the next Democrats in line - Sens. Spark M. Matsunaga of Hawaii, and Daniel Patrick Moynihan of New York - may not be interested in it. Third in line is Sen. Max Baucus, D- Mont., who wants the post.

FOREIGN RELATIONS - Sen. Claiborne Pell, D-R.I., would replace Sen. Richard G. Lugar, R-Ind. as chairman. The committee's limited jurisdiction over trade matters includes funding for the Overseas Private Investment Corp. and oversight of the U.S. Foreign Service. Sen. Pell's principal interests lie in areas that include arms control and the law of the sea. He also supports U.S. trade promotion efforts and may have oversight hearings on the Foreign Services Act of 1980.

JUDICIARY - The Senate Judiciary Committee could be a source of major grief for the insurance industry. The key player on a reconstituted Antitrust Subcommittee would likely be Sen. Howard Metzenbaum, D-Ohio, who has been in the forefront of the movement to repeal the McCarran-Ferguson Act. The act provides the insurance industry's antitrust exemption and also makes insurance a matter of state rather than federal regulation.

The result, when combined with the changes at the Commerce Committee that will make it difficult for tort reform legislation to surface there, could be a major threat to the insurance industry. The worst case scenario would be a result in which federal regulation of insurance was enacted but without any quid pro quo of a federal product liability law.

Sen. Metzenbaum could also be expected to actively oppose many of the Reagan administration's antitrust proposals. He has strongly opposed administration attempts to lessen strictures against vertical restraints to

allow manufacturers to control distribution and pricing of products. The question of who would chair a Democratic Judiciary Committee is unknown since Sen. Edward Kennedy, D-Mass. senior member on both Judiciary and on Labor, has not disclosed his intentions. If he chooses Labor, Sen. Joseph R. Biden Jr., D-Del. would become the Judiciary chairman.

LABOR AND HUMAN RESOURCES - If Sen. Kennedy decides to be chairman of the Judiciary Committee rather than this committee, Sen. Metzenbaum would succeed the current chairman, Sen. Orrin Hatch, R-Utah. Either Democrat is bound to take a more pro-labor stand on issues than the Republicans did under Sen. Hatch. That could create major problems for anticipated administration initiatives such as repealing the minimum wage requirement for teen-age workers and rewriting the Rail Labor Act.

Attempts to curtail the ability of employers to withdraw overfunding of pension plans would get a boost and there would be fierce debate over proposed changes in multi-employer pension legislation needed to implement an agreement in this area reached between the trucking industry and the Teamsters Union.

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