Overhauling the costly federal Superfund program is the highest priority for the property/casualty insurance industry, even though provisions to eliminate liability for pre-1987 pollution have been dropped from proposed legislation.

The legislation, to be introduced this month, was changed after opponents of ending all liability predicted a shortfall of $300 million to $800 million for future cleanups of Superfund waste sites.The concern comes at a time when Republicans have pledged no new taxes and when Congress is cutting appropriations for the Environmental Protection Agency. Superfund - in particular, how to find enough money to persuade legislators to drop retroactive liability - has been a hot topic of discussion among members of the the Council of Insurance Agents and Brokers and the National Association of Casualty and Surety Executives.

''It is our No. 1 legislative priority this year," said Joel Wood, the council's vice president of government affairs. "More so than any other issue, there is a sense within the P/C community that we must all hang together or we will hang separately. I don't expect anyone to be straying from the pack on this."

That wasn't the case last year, however, when the Superfund proposal with the best chance of passage contained an $8.1 billion tax on the insurance industry.

The tax, which would have been spread over 10 years, was designed to pay for settling most of the cases backlogged in state and federal courts across the country.

Only one insurance-industry group, the American Insurance Association, agreed to support the reform bill, which had the backing of the Clinton administration. The bill died in the last days of the 103rd Congress, but rancor against the AIA remained.

With the Republican-dominated 104th Congress pledging not to raise taxes, reform plans put the emphasis on removing polluters' liability, shifting control of some Superfund sites to the states, and cleaning up sites using more realistic standards.

"After last year's debacle, there is a widespread recognition that, given the stakes and the uphill battle we face, we can't go our own ways," said Mr. Wood. Insurance companies, agents, brokers and reinsurers have joined forces this year in an umbrella group called Superfund Reform '95.

Superfund, which expires in December unless reauthorized, was created in 1980 to clean up a few sites at a cost of $1 billion to $2 billion over five years. However, costs currently exceed $25 billion, and fewer than 220 of the 1,410 sites on the National Priorities List have been cleaned up, according to a recent report by the American Academy of Actuaries.

The academy estimates the total number of Superfund sites to be cleaned up will be 2,000, rather than the 3,000 to 4,500 estimated by several groups, at a cost of less than $100 billion, instead of $150 billion to $165 billion. Lower costs to Superfund mean lower taxes for chemical and petroleum companies and lower legal costs for their liability insurers.

With the projected costs so high, Republicans were eager to join forces on a reform that would reduce costs without additional increases in taxes. A bill, to be introduced around Columbus Day, was unveiled last month by Rep. Mike Oxley, R-Ohio, chairman of the Commerce Committee's Subcommittee on Commerce, Trade and Hazardous Waste Materials.

Rep. Oxley's Senate counterpart, Robert Smith, R-N.H., chairman of the Environment Committee's Superfund, Waste Control and Risk Assessment subcommittee, introduced a similar measure last month.

Their proposals are virtually identical except for certain "fair share" liability provisions. The Oxley plan, which had dropped liability for all pre- 1987 polluting, now exempts only municipal landfills and those who have been found to be responsible for less than 1 percent of the pollution.