The highest-ranking woman at the White House yesterday defended President Carter's record in placing women in high-level positions but said she disagreed with a reported decision to deny two of Carter's female supporters the jobs they sought.

Margaret (Midge) Costanza, a special assistant to the President, was asked about reports that Carter supporter Barbara Blum and Mary King were told last week that they were not qualified for top administration jobs.

The report, in the Chicago Sun Times, said that presidential assistant Hamilton Jordan summoned both women to the White House last Friday. Jordan told Blum she could be a member, but not the chairman, of the Council on Environmental Quality, and told King that she could be a deputy, but not the head, of Action, the agency that includes VISTA, the Peace Corps and other volunteer organizations, according to the report.

"Hamilton might be coming from a personal viewpoint," Costanza said. "Mary King is a very capable woman. Barbara Blum is a very capable woman. I do not share the opinion of Hamilton Jordan."

Costanza made the remark at a breakfast meeting with reporters. After the breakfast, she said she had not read the report about King and Blum and was "shocked" to learn of it. She said she planned to discuss it with Jordan.

During Carter's campaign, Blum was the deputy campaign director, working in Atlanta with Jordan. She later became director of the Carter transition office in Washington.

King was one of Carter's earliest supporters and organized women's groups behind his candidacy. Her husband, Washington psychiatrist Peter Bourne, has been named, special assistant to the President for mental health and drug abuse.

King and Blum are two of the most celebrated cases involving Carter's record in fulfilling his campaign pledge to give women and minority group members a much larger share of high level government jobs. Carter has admitted his difficulty in finding and convincing women to serve in the administration and, in turn, has been sharply criticized by feminist groups for not living up to his campaign rhetoric.

Defending the President's overall record, Costanza said, "I don't agree that women have not had a fair shake." She said Carter has instructed his Cabinet secretaries to conduct an "ongoing search" for qualfied women and minority group members, in effect asking them "to please help me keep my pledge."

But she said the process of filing administration jobs throughout the executive branch has been slow, "they are not really fully staffed," she said.

Constanza's $44,600-a-year White House job is to deal with special interest groups. She pledged to cut the size of the staff that deals with special interest groups from 30, as it was in the Ford administration, to nine.

Costanza also said that she will seek to bring Carter into contact with people who both agree and disagree with him, and that the President's often-stated desire to have wide ranging public contacts will not be "cosmetic."

"Either I will function as a window for the President or I won't be in Washington," she said.

Brown, who in 1968 was youth chairman of the Eugene McCarthy presidential campaign, this year was an early supporter of Carter. He also wrote an article for The New York Times urging liberals not to support the McCarthy candidacy.

He will take over a $100 million-a-year agency that was created from disparate volunteer programs by the Nixon administration and that has frequently been best with both management andmorale problem.