A determined Senate Budget Committee was running $2.4 billion ahead of President Reagan's budget-cutting pace last night but flinched from a proposal that would have scaled back cost-of-living increases in Social Security and other retirees' benefits.

By last night, the committee had proposed cutting cut more than $35 billion from existing programs. It expects to finish work today and send the unprecedented package to the Senate next week.

As it worked to complete a list of budget-cutting instructions for other committees, the budget panel also gave some indication of its priorities by proposing to reduce the president's proposed cuts for the Export-Import Bank and make up the difference by cutting even deeper than he wants into programs for subsidized housing and community development.

Later, it proposed giving Reagan $711 million more than he wanted for education, youth job training and programs for the handicapped -- a partial concession to the Senate Labor and Human Resources Committee, which voted earlier to add more than $2 billion to Reagan's spending plans for these and related services.

It also gave Reagan $244 million more for the Women, Infants and Children (WIC) feeding program but refused to restore cuts in the food stamp and school lunch programs.

Earlier, it voted to go beyond Reagan's proposed cuts in unemployment insurance by suggesting that, as of 1983, benefits be limited to applicants who have worked 20 weeks in a year. Such work-history standards now vary from state to state. The proposal would save $900 million to $1.7 billion in 1983, depending on the unemployment rate, and reduce the number of recipients by 20 per cent, according to committee estimates.

These Senate budget votes came as the House dairy subcommittee rejected a Reagan plan to curtail milk price support payments, and the House Ways and Means Committee agreed to a tax cut of the size he has proposed next fiscal year, but only if spending is cut as much as he recommended. [Details, Pages A7 and A3.]

The Democratic minority on the Senate Budget Committee, rancorously divided on many key issues, finally pulled together to try to keep the $122 per month minimum Social Security benefits and students' benefits under Social Security, just for people now receiving the benefits.

"Do you really want to cut benefits to 1.1 million old people with income of less than $3,100 a year?" asked Sen. Lawton Chiles (D-Fla.). The answer appeared to be yes, as the Chiles-sponsored proposal failed on a party-line vote of 9 to 11. Defenders of the Reagan proposal note that those who lose if the minimum benefit is cut can turn to the federal welfare program for the aged and disabled.

And even the Democrats in effect fell in line behind Reagan in refusing to go along with their ranking minority member, Sen. Ernest F. Hollings (D-S.C.), who moved to scale back the $22 billion in cost-of-living increases that recipients of Social Security, veterans benefits and federal pensions will receive in 1982 -- a figure that Hollings said will exceed $272 billion for the 1982-1986 period.

Republicans on the committee had been pushing for such a change until Tuesday when Reagan emphatically restated his opposition to it, saying he didn't want controversy over Social Security to undercut momentum for his budget cut program.

Four Republicans broke with Reagan to support Hollings' proposal to save about $7 billion in fiscal 1982 by delaying cost-of-living payments for three months and pegging increases to a wage index rather than the Consumer Price Index if wages rise less than prices during the period. But the proposal lost, 13 to 5, when no Democrat supported it.The Republicans were Mark Andrews (N.D.), Steven D. Symms (Idaho), Bob Kasten (Wis.) and Dan Quayle (Ind.).

Several Democrats said they would have supported the move if it was joined by Reagan. Until it is, any such effort is "doomed to failure," said Sen. Gary Hart (D-Colo.). Moreover, he added, the federal budget will never be balanced until the cost of these so-called "indexed" benefits is brought under control.

Republicans indicated that Reagan, despite his opposition to changing the cost-of-living payments for retirees, may seek some change in the future. "There is a time, and it need not be too distant, that we can reconsider," said Budget Committee Chairman Pete V. Domenici (R-N.M.).

The committee's work constitutes the first step in congressional action on Reagan's proposal for $48.6 billion in spending cuts for 1982. The house and Senate Budget committees will propose dollar savings that each legislative committee in the two bodies are to achieve. After Senate and House act on these instructions, it will be up to each legislative committee to decide exactly which program in its jurisdiction are to be cut, and how. However, the intended cuts are so big in many cases that the legislative committees may have little choice but to follow the budget panels' program-by-program suggestions.

In all, the Budget Committee figures that it can only squeeze about $34 billion in savings from the Reagan list into its so-called "reconciliation" instructions, in part because Reagan has overestimated some savings and in part because some of the proposals have to be handled separately. Hence the committee is looking for even more cuts than Reagan offered it.

But it also went even further than Reagan, in some cases, in shifting the bueden of the cuts toward the poor.

Under a proposal from Sen. Nancy L. Kassebaum (R-Kan.), it voted 16 to 4, with the hard-core of liberal Democrats in dissent, to restore one-third of the cuts that Reagan recommended for Export-Import Bank loans, at preferential interest rates, to customers of U.S. exporters. The loss would be more than made up by even larger cuts than Reagan proposed for subsidized housing for the poor and community development funds.

The proposal by Kassebaum, whose state is a major producer of airplanes that are sold abroad with the held of the Ex-Im Bank, would restore $14 million of the $41 million cut that Reagan proposed for 1981, $110 million of the $222 million cut for 1982 and $357 million of the $765 million cut for 1983, according to Kassebaum.