President Carter announced seven more sub-Cabinet nominations yesterday, and chose Georgia Supreme Court Justice William B. Gunter, 57, to be his special negotiator in the disputed claims of two Indian tribes to several million acres in Maine.

The President also had a third and final set of talks with British Prime Minister James Callaghan, and said the discussions "were of great benefit to both our countries."

After seeing Callaghan off from the South Lawn of the White House, Carter said the thinks the economic summit he is scheduled to attend in London in May "will be much more substantive and productive now that we've explored possibilities there."

The White House disclosed no specifics about the 75 minutes of talks yesterday morning.

Callaghan told reporters he believes the Soviet Union remains committed to detente and the West should not panic over growing Soviet military might.

The British prime minister also said Carter's efforts to focus attention on international human rights are based on a "well-thought-out philosophy."

Carter also confirmed that he would make former Democratic National chairman Robert S. Strauss his special representative for trade negotiations.

The White House said Strauss, a Dallas attorney who served as Democratic party chairman until January, will be allowed some exceptions to Carter's conflict-of-interest guidelines because he has a 30-per-cent stock interest in the family-owned Strauss Broadcasting Co. and 35 per cent of his investments are stock of the Valley State Bank.

Carter is permitting Strauss to put all his holdings into a blind trust with the understanding that he will disqualify himself from acting on any matters that would affect the interests of the bank or the broadcasting company.

Strauss will draw a salary of $66,000 a year and have ambassadorial rank in his new post.

Gunter, a longtime personal firend of Carter, was scheduled to return to private law practice at the end of March.

The Justice Department recommended to Carter last month that he name a special representative to resolve the Maine Indian dispute.

AA federal court ordered the department in 1972 to file suit against Maine on behalf of Penobscot and Passamoquoddy claims that 12.5 million acres were taken in violation of a 1790 law.

On Feb. 28 the department said if an out-of-court settlement is not reached by June 1, it will press a suit supporting scaled-down claims of up to 5 million acres.

The seven sub-Caninet nominations Carter sidhe will make:

Richard Warden, 45, a former lobyist and assistant legislative director for the United Auto Workers, as assistant secretary of health, education and welfare for legislation.

Francis X. Burkhardt, 32, director of economic research for the International Brotherhood of Painters and Allied Trades (AFL-CIO), to be assistant secretary of labor for labor-management relations.

Eula Bingham, 47, associate director of the University of Cincinnati's Department of Environmental Health, to be assistant secretary of labor for occupational safety and health.

Alexis M. Herman, 29, director of a minority women employment program in Atlanta, as director of the Labor Department's Women's Bureau.

Arnold Packer, 42, chief economist for the Senate Budget Committee, as assistant secretary of labor for policy, evaluation and research.

Lawrence B. Simons, president of LBS Construction Co. of New York City, to be assistant HUD secretary for housing.

Former Baltimore Housing Commissioner Robert Embry to be assistant HUD secretary for community development and planning.