Paul C. Warnke was sworn in yesterday as director of the Arms Control and Disarmament Agency and as President Carter's chief negotiator in strategic arms limitation talks with the Soviet Union.

"I have the feeling that this ends one of the longest running soap operas," Warnke said after taking the oath of office from U.S. District Court Judge Gerhard A. Gesell.

The comment - a reference to the controversy sparked by his nomination - prompted laughter from Carter and other supporters at the ceremony in the White House Rose Garden.

Warnke was confirmed Wednesday as Carter's chief SALT negotiator on a 58-to-40 vote in the Senate and as director of the arms control agency on a 70-to-29 vote. His confirmation had been opposed in massive mail and telephone campaigns and at Senate hearings by conservatives who said he would be too soft in arms limitation talks with the Soviets.

Carter said Warnke "weathered . . . in good spirits" the "tough cross-examination and the unwarranted criticism." The President said he never doubted that Warnke was the best man for the disarmament post and, as if to demostrate his confidence, he announced that Warnke would accompany Secretary of State Cyrus R. Vance when he leaves for Moscow.

Carter said Vance and Warnke will present to Soviet leaders this country's "fairly final position" on SALT negotiations. The position is being completed this week by the National Security Council, the President said.

Carter said he believes the Soviets attach a "great deal of importance to the Vance-Warnke trip. He did not elaborate.

In other matters yesterday, White House press secretary Jody Powell said Carter will continue to speak out for human rights despite a warning in the Soviet newspaper Pravda that Carter's support of Russian dissidents could hurt arms talks.

"I think our position on human rights is clear," Powell said. "As we said at the outset, we will act-according to our best judgement, which is supported by the people of this country.

"In cases where public efforts are appropriate, we will so act. Where private efforts are appropriate, we will so act."

Powell also said that Charles L. Schultze has given up his position as cochairman of the Economic Policy Group, one of three economic posts Schultze has held under Carter.

Powell said Treasury Secretary W. Michael Blumenthal will become "the sole chairman" of the group, which is responsible for drafting economic policy recommendation for Carter.

Powell said the charge was made at the request of Schultze, who felt there was a conflict with his role as cochairman of the group and his duties as personal economics adviser to the President and chairman of the Council of Economic Advisers. Powell would not elaborate.

The press secretary said Schultze would continue to serve as a member of the policy group.

Carter said yesterday he will nominate Daniel H. Brill, a Maryland credit company executives, to be an assistant secretary of the Treasury Brill, 58 is executive vice president of Commercial Credit Co. in Baltimore.If nominated and confirmed by the Senate he would be in charge of the Treasury Department's economic policy staff.