House Democrats exhibited the first official signs of Proposition 13 fever yesterday by ordering the Ways and Means Committee to reduce a Social Security tax increase voted by the last Congress, but which is not scheduled to take effect until 1981.

After the vote, Rep. A1 Ullman (D-Ore.), chairman of Ways and Means, predicted that there will be no Social Security tax increase in 1981.

The voice vote by the caucus came on a motion by Rep. Christopher Dodd (D-Conn.) But the Democrats left unresolved how to cut the scheduled tax increase without avoiding future cuts in Social Security benefits.

In other action, the Democrats rejected a proposal that would have required the caucus to decide whether a member indicted for abuse of powers of his office should be allowed to continue as chairman of a committee or subcommittee.

Legislation approved by Congress in 1977 calls for a sharp increase in the payroll tax rate in 1981 and a further increase in the wage base against which the taxes are paid.

The Democratic Caucus approved a resolution last year asking Ways and Means to roll back scheduled Social Security tax increases, but the committee ignored it. Dodd said he considers his resolution to be stronger.

Ullman said no decrease will be enacted this year, adding, "It is going to take a year's worth of hard work."

House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) said that while he "personally" is not in favor of a Social Security tax rollback, Ullman has "made a commitment" to a complete review of Social Security taxes and benefits.

A spokesman for Ullman, John Sherman, said the question is "the degree to which the bill will roll back the 1981 tax jump," a degree he said will depend on the economy and other factors.

Sherman also said that while Ullman believes President Carter's proposals to trim back several popular Social Security benefits will not be approved this year, he does not consider tham all bad. Carter estimated the changes would save $600 million in fiscal 1980.

Sherman said Ullman fist wanted to "isolate" committee work on limiting federal disability benefits to discourage abuse before getting into "the Pandora's box" of Social Security taxes and benefits.

In offering his resolution to the caucus Dodd said a person earning $22,100 paid $332 more in Social Security taxes last year and that the tax will jump "by that much more in 1981."

In the other action, the caucus rejected one "ethics" proposal and put another off for two or three weeks.

Rejected was a proposal by Rep. Elizabeth Holtzman (D-N.Y.) to have the caucus vote on whether an indicted member of Congress changed with a felony that involves abuse of powers of his or her office should continue to serve as a committee or subcommittee chairman.

Rep. Frank Thompson (D-N.J.) successfully amended the proposal to apply only to convicted or censured chairmen.

Rep. Daniel Flood (D-Pa.) is on trial on bribery charges and Rep. Charles Diggs (D-Mich.) is appealing his conviction of taking salary kickbacks.

Discussion of a proposal by Rep. Peter Kowtmayer (D-Pa.) to have the Committee of Standards of Official Conduct make a recommendation in 20 legislative days as to what to do about a convicted member whose appeals have been exhausted was postponed until the next caucus meeting.