Senate Republican leaders have prepared a list of spending cuts and tax increases that hinges on a two-year freeze on inflation adjustments for Social Security and other benefit programs to reduce deficits to $20 billion by 1985.

But sources said the leaders have not agreed to propose elimination or even modification of cost-of-living increases for any of the big benefit entitlement programs, and Senate Finance Committee Chairman Robert J. Dole (R-Kan.) said yesterday that he doesn't think any kind of Social Security freeze is politically achievable.

"I think that's where the president would say no, no, no," said Dole, adding, however, that it will be "hard" to get to the leaders' deficit targets without touching Social Security inflation adjustments.

The list was described by sources as including deficit reductions of about $400 billion over the next three years, with $2 in spending cuts for each $1 in new revenue raised through taxes. It does not specify what taxes would be raised but reportedly envisions mostly loophole-closing, such as repealing the new corporate tax-break leasing provision and stiffening minimum taxes for individuals as well as corporations.

The list also includes a three-year freeze on domestic programs financed through annual appropriations, which would save $7 billion next year, and a $10 billion reduction in President Reagan's proposed defense spending increase for the year. Savings from defense would total $40 billion to $45 billion over three years.

No pay increase for federal workers would be provided next year.

There would be savings from entitlement programs other than Social Security, such as food stamps, Medicaid and Medicare, through tightening of eligibility standards and other cost-cutting measures.

The list--or "working sheet," as the leaders call it--was prepared over the past week as a kickoff point for development of major revisions in Reagan's budget, which Congress has indicated is unacceptable in its present form. Sources went out of their way to deny that it was a finished product, especially in regard to entitlement program changes. "They're just saying this is a possible way it could be done," said one source.

The list has been submitted to the White House and is scheduled to be presented for discussion at a policy luncheon of all Senate Republicans on Tuesday.

Depending on how the Republicans receive it, the Senate leaders plan to begin talks with senior Democrats, including ranking members on the major Senate fiscal committees, in hopes of putting together a bipartisan budget draft, according to Dole and others.

The goal is to get an economic package through Congress by June, Dole said.

The list--as assembled by Senate Majority Leader Howard H. Baker Jr. (R-Tenn.), Budget Committee Chairman Pete V. Domenici (R-N.M.), Appropriations Committee Chairman Mark O. Hatfield (R-Ore.), Sen. Paul Laxalt (R-Nev.) and Dole--would almost double Reagan's proposed deficit reductions over the next three years. Reagan proposed $240 billion in reductions, compared to the Senate leaders' $400 billion.

The Senate list would produce a deficit of $86 billion next year and $20 billion by 1985, according to sources. The leaders are said to want a deficit of no higher than $35 billion for that year. Reagan projects a deficit of $91.5 billion next year, based on $56 billion in spending cuts and revenue increases that Congress is balking at. But the Congressional Budget Office calculates Reagan's 1983 deficit at $121 billion, rising to $140 billion by 1985.

In addition to the spending cuts and tax increases, the senators are reportedly anticipating $40 billion to $50 billion in reduced interest costs stemming from the lower deficits. They are also assuming the management savings that the administration projected in its budget, sources said. Cost-of-living increases for entitlement programs, especially Social Security, is one of the biggest potential sources of savings. Domenici has said a freeze just for 1983 would save $60 billion through 1985. But the inflation adjustments are also regarded as the major sticking point on the list. Both Reagan and House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) have opposed any changes in Social Security this year, and they would probably be difficult to get in an election year anyway.

Social Security accounts for about 80 percent of cost of inflation-indexing for entitlement programs, making entitlement program savings difficult without touching Social Security. A partial freeze or less drastic modification is possible, but even that "is very much in doubt," said a source close to the leadership.