WASHINGTON (AP) _ A Senate committee, heeding criticism of civil rights activists, on Tuesday rejected President Reagan's nominee for chief enforcement officer at the Equal Employment Opportunity Commission.

Three Republicans joined the seven Democrats on the Labor and Human Resources Committee in the 10-5 vote against the nomination of Jeffrey Zuckerman to move from chief of staff to general counsel of the commission.

Civil rights activists argued that Zuckerman's opposition to affirmative action disqualified him from heading the commission's enforcement division and groups representing the elderly questioned his dedication to protecting older workers from age discrimination.

The vote, effectively killing Zuckerman's nomination, marks the second time in a year that the Senate has rebuffed a presidential choice for an administration position because of civil rights considerations.

The Senate Judiciary Committee refused last June 27 to recommend confirmation of Assistant Attorney General William Bradford Reynolds, head of the Justice Department's civil rights division, as associate attorney general.

''As it was with Brad Reynolds,'' the vote marked ''a strong bipartisan rejection of extremism on civil rights,'' said Ralph Neas, director of the Leadership Conference on Civil Rights.

''His actions repeatedly were inconsistent with the fair employment laws as passed by Congress and as interpreted by the courts,'' Neas said.

Zuckerman said in a statement he was ''deeply disappointed'' by the vote. ''But I take solace from the fact that when Justice (John Marshall) Harlan said in 1896 that the Constitution of the United States is colorblind, he was voted down 8-1,'' he added.

''We are reassessing the situation,'' said White House spokesman Albert R. Brashear. ''We realize we didn't lose by one vote.''

EEOC Chairman Clarence Thomas said in a statement issued by the commission that he was ''disappointed and dismayed that his (Zuckerman's) nomination was not confirmed.''

''Have no doubts that this commission intends to continue implementing its enforcement policies with or without a confirmed general counsel,'' Thomas said.

Thomas, whose term as EEOC chairman expires June 30, was nominated earlier this month for a second term to head the agency.

During brief debate on the Zuckerman nomination, Sen. Howard Metzenbaum, D- Ohio, said, ''Whoever fills that position should have a commitment to enforcing civil rights legislation.''

''It's astounding the administration would nominate someone who has never litigated'' a civil rights case, Metzenbaum said. ''He has never dealt with the reality of how civil rights statutes are applied.''

Zuckerman acknowledged at his March 4 confirmation hearing that his opposition to hiring goals and timetables put him in ''fundamental disagreement'' with civil rights groups.

But he promised to ''litigate every case'' to protect individual victims of job discrimination and use ''everything we have, including contempt'' proceedings against employers who discriminate.

Sen. Orrin G. Hatch, R-Utah, the panel's chairman, said Zuckerman's pledge to ''expand the EEOC caseload'' demonstrated his commitment to civil rights enforcement.

Hatch said there was case law to support Zuckerman's opposition to hiring goals and timetables, which are opposed by the Reagan administration.

''If the Supreme Court would define these areas a little more'' Zuckerman would enforce the law, Hatch said.

On Monday, the high court threw out a Michigan affirmative action plan that protected the jobs of black teachers at the expense of whites with more seniority. But justices wrote five opinions expressing support for affirmative action plans in general. Sen. Edward Kennedy, D-Mass., said Zuckerman had worked with the Office of Management and Budget to ''undermine EEOC'' after its promulgation of regulations to allow workers over age 65 to accrue pension benefit credits.

Three GOP members, Sens. Charles Grassley, R-Iowa, Robert Stafford, R-Vt., and Lowell P. Weicker, R-Conn., joined with the committee's seven Democrats to kill the nomination. Sen. Paula Hawkins, R-Fla., abstained.