Rep. Michael D. Barnes (D-Md.) challenged White House aide Linda Chavez yesterday to repudiate Justice Department efforts to weaken a major affirmative action program, saying that affirmative action will be a key issue in the U.S. Senate race in Maryland if Chavez is the Republican nominee.

At a Capitol Hill news conference, Barnes, a Democratic candidate for the Senate nomination, said Chavez was hostile to affirmative action programs when she was staff director of the U.S. Civil Rights Commission.

He said he was encouraging her to oppose a proposal by Attorney General Edwin Meese III to eliminate penalties for federal contractors who fail to meet hiring goals for women and minorities.

Labor Secretary William E. Brock and other cabinet moderates strongly oppose the Meese proposal.

Chavez, who is leaving her job as White House public liaison director Monday and is expected to announce her candidacy for the Senate in late February, said she had "always been a strong supporter of affirmative action," and has urged minority recruitment and job training.

Questioned after Barnes' news conference, she said that she supported the 1965 order by President Lyndon B. Johnson directing federal contractors to make good faith efforts to hire more minorities and female employes. But she said that the Labor Department had enforced the executive order so rigidly that the hiring goals have become quotas.

Chavez, one of the highest ranking Hispanics in the administration, said that as a White House aide she could not comment on her position in the internal Reagan administration battle. But she said she is strongly opposed to quotas, and she issued her own challenge for Barnes to state his position on quotas.

Barnes spokesman Bill Bronrott said that Barnes is opposed to quotas.

Republicans said the attacks against Chavez appeared premature, because she had not yet declared. They speculated that the press conference was aimed at Rep. Barbara Mikulski (D-Md.), who has been leading Barnes in polls. Mikulski is better known in the black community in Baltimore than Barnes and has the support of many women's groups.

Barnes said he called the news conference now, before a final White House decision is made, because it is important for voters to know if Chavez, as White House public liaison director, is conveying to the president the wide array of opposition.