The Clinton administration and Republican leaders in Congress are moving toward a comprehensive political deal designed to overcome a $34 billion budget impasse blocking a historic, six-year surface transportation infrastructure spending package.

In a series of closed-door meetings on Capitol Hill Tuesday and Wednesday, Democrats and Republicans sketched out competing proposals to trim the ambitious $217 billion highway bill's price tag by $18 billion, while assuring record increases in new federal funding for state construction projects.A combination of real spending cuts elsewhere and creative math would be used to make up an additional $16 billion needed to keep the highway bill within last year's balanced-budget agreement.

''The administration has come a long way. They came with a comprehensive offer,'' Sen. Max Baucus, D-Mont., a leading Senate Democrat on the highway bill said after meeting Tuesday with Office of Management and Budget Director Franklin Raines and Transportation Secretary Rodney Slater.

Administration officials met again Wednesday with Sen. John H. Chafee, R-R.I., chairman of the Senate public works committee, to present the White House proposal. A Senate Republican leadership meeting was scheduled by Majority Leader Trent Lott, R-Miss., later Wednesday.

Mr. Baucus said the administration's offer ''gets close to the budget and relies on the principle that we spend what comes in'' to the highway trust fund from fuel taxes paid principally by auto drivers and commercial truckers.

A spokesman for Mr. Chafee was unable to describe the public works chairman's meeting with administration officials in detail, but confirmed that it involved budget issues surrounding renewal of the Intermodal Surface Transportation Efficiency Act of 1991, which expired last week.

''This is the first and most important domino that needs to fall in a long line of dominoes,'' Mr. Chafee's spokesman said. Mr. Slater was also reluctant to describe the administration's offer in detail on Tuesday night. But he described it as an effort to reach a political deal with Congress that would pave they way for enactment of the legislation.

''We visited with all the chairmen in an effort to get an understanding of their needs, and this is a comprehensive offer that attempts to address those needs,'' Mr. Slater said.

Staff sources said the administration is proposing a $219 billion highway and transit spending package that would be spread out over seven years rather than six. In the first couple of years, the administration plan would not spend as much revenue as is expected to come into the highway trust fund. Then in 2000 it would phase in a guarantee that highway spending would equal the prior year's gas and diesel tax receipts. The combined budgetary effects of the three moves would reduce from $34 billion to $13.5 billion the amount of spending cuts Congress would have to achieve elsewhere in order to stay in line with last years historic, bipartisan balance budget agreement.

The administration is proposing to cut health benefits for tobacco-related illnesses of veterans, but believes it has a way to placate veterans groups by reforming the program.

Republican leaders also were expected to come up with budget proposals for the highway bill Wednesday afternoon.

The budget baseline projects Istea program spending of $170 billion over six years, while the House bill projects $205 billion in outlays. Rep. John Kasich, R-Ohio, chairman of the House Budget Committee, has previously proposed a phase-in of the trust fund spending guarantee, meaning the administration proposal is likely to find support with budget hawks.