Republican officeholders, nervous about public reaction to President Reagan's proposed Social Security cutbacks, voted at an informal party meeting today to assure "those who are now concerned that no particular age group or segment of our population will sustain an unfair burden" of protecting the retirement system from bankruptcy.

In Washington, meanwhile, Health and Human Services Secretary Richard S. Schweiker said Reagan is willing to compromise on his Social Security proposals. "We would certainly strongly consider working out a bipartisan bill," Schweiker said in an appearance on the "UPI Roundtable" broadcast.

The language adopted at the Republicans' tidewater Conference, attended by 117 GOP members of the House and Senate, governors and other statewide officials, avoided any direct repudiation or endorsement of Reagan's proposal for a sharp reduction starting next year of benefits for those who retired before age 65.

But Rep. Carrol Campbell (R-S.C.), one of the drafters of the final statement, capsulized the mood when he said, "There are many people upset and disturbed" by what they have heard of the Reagan plan.

"Those on the brink of retirement years think the rug is being pulled from under their feet."

In his message on the financial crisis threatening the Social Security trust fund, Reagan proposed protecting benefits and cost-of-living allowances for all present recipients but suggested cutting benefits by almost one-third for those who choose early retirement in the future. That provision has stirred great controversy and was denounced by House Speaker Thomas P. (Tip) O'Neil Jr. (D-Mass.) as "stone-hearted."

The Republicans rallied behind the president, up to a point. The resolution said the fiscal problems now facing Social Security are a result of "the abysmal neglect of past Democratic-dominated Congresses, which have accelerated the benefits far beyond the ability of the system to pay for them." a

Former party chairman Bill Brock, now the administration's special trade representiative, said statements like O'Neill's are a contemptible exercise in political hypocrisy."

But while commending Reagan for "properly focusing national attention" on the Social Security system's financial problems and joining his opposition to any boost in payroll taxes, the Requblican officeholders were plainly looking nervously over their shoulders at their constituents on this issue.

Sen. Charles H. Percy (R-ILL.) said that three-fourths of the questions he received on a radio call-in show this week suggested that people thought Reagan was "just whacking back benefits in a railroading kind of proposition."

Actuarial calculations indicate that the Reagan proposals eventually would reduce Social Security benefit outlays by nearly one-fourth, and would save twice as much as the program needs to operate in the black. Budget director David A. Stockman attempted to downplay those figures in a news conference today, saying that the actuarial numbers, calculated over a 75-year period, and "very artifical and misleading."

And Schweiker indicated that Reagan would be happy to consider different approaches to the problem if Congress wants to offer them up. "Certainly you're going to have to do some give-and-taking," he said . ". . . I think we're certainly willing to look at a reasonable proposal and blending of different ideas."

The Tidewater Conference was started in 1978 by Sen. Bob Packwood (R-Ore.), partly as a social weekend for Republicans and partly as a forum for arguing out divisive issues within the party in an informal atmosphere. This is the first time it has met with a Republican in the White House, and the participants were sensitive to any suggestion that they might be at odds with the administration.

In addition to Brock, two other Cabinet members -- Interior Secretary James G. Watt and Energy Secretary James B. Edwards -- attended, and White House political counselor Lyn Nofziger was monitoring the proceedings.

Earlier, a group of Republican governors won a tactical victory when they succeeded in removing from a draft-resolution on block grants a specific reference to giving states "responsibility for the maintenance of health, education and welfare."

The governors, led by Richard Snelling of Vermont and Lamar Alexander of Tennessee, said they supported Reagan's pending proposals to merge more than 100 separate, categorical programs into seven block grants for health, education and community development.

But when it came to welfare, Alexander said, "the president has one view and most governors have another." Reagan for many years has urged that the basic income-support programs be turned over to the states, while the National Governors Association equally long has called for federalization of welfare.

With backing from Sen. David Durenberger (R-Minn.), the chairman of the Senate Inter-Governmental Relations subcommittee, the governors pushed through a resolution urging a "sorting out of obligations and capacities as they are most appropriate at each level of government. . . ."

The conference kicked off with a discussion of trade policy. Brock offered language stressing the need for carrying out U.S. trade laws in a way that builds domestic political support for the goal of free trade.

But he backed off when a number of House members said that implied protectionist measures. Brock denied that was his intention, and the final language said the goal of "reduced trade barriers" could be reached only through "reciprocity and equity."

The conference also reaffirmed the Republican Party platform's pledge of across-the-board tax cuts.