Sen. Frank Church (D-Idaho), incoming chairman of the Senate Foreign Relations Committee, said yesterday he expects public hearings early next year on the appointment of retired Lt. Gen. George M. Seignious to head the Arms Control and Disarmament Agency, and that he sees no reason why a military man cannot perform well in the job.

While withholding final judgment until after detailed questioning at the hearings, Church reported a favorable impression after a private talk with Seignious.

"It's clear that he's sufficiently knowledgeable and committed to the objective of the agency," said Church. He added that in some circumstances a military background can lend credibility and impact to arms control views, as in the case of former president Eisenhower.

Seignious' nomination has com under attack by some individuals and organizations in both the activist and conservative wings of the arms control field. The activists have expressed fear that Seignious' military attitudes will weaken anti-arms positions in the agency.

Some conservatives, on the other hand, expressed fear that Seignious will lend a comforting military tone to a new strategic arms limitation treaty (SALT) and other arms control ventures.

Seignious moved into his job as arms control agency director Monday under a recess appointment from President Carter. This will permit him to serve until his nomination is considered by the Senate next year.

In his only public utterance since being sworn in late Monday, Seignious told a conference of women's organizations at the State Department that he has come to "a city that is reaching for my blood already."

His brief statement called for public support of efforts to place "some limit and some top on the deadly peril" of the nuclear arms race, and said he planned to improve the "quality of excellence" and "level of credibility" of his agency.

In a remark he has repeated in talks with senators and some officials of the agency, he said that "arms control is in fact an internal part of our national security planning and an integral part of our national posture throughout the world."

Informed sources said Seignious elaborated on Capitol Hill by saying that arms control should be "fully integrated" into overall national security policy. He reportedly said that the arms control agency need not always be in conflict with the Pentagon, and that in some case negotiated agreements could do more than military programs to protect U.S. national security. One source said Seignious also suggested if the military budget goes up as now anticipated, perhaps the arms control budget should increase as well.

Seignious also reportedly told law-makers that the United States should modernize its strategic arsenal as permitted under the terms of a SALT II agreement, while seeking to negotiate additional quantitative and qualitative limits in a future SALT III treaty with the Soviet Union.

According to aides, he has given no indication whether he will seek to make major personnel shifts within the arms control agency. His only shift so far is to bring in Norman Clyne, a former Army colonel and former executive secretary of the U.S. delegation to the SALT II talks, as executive secretary of the agency. CAPTION: Picture, Presidential aides Zbigniew Brzezinski and Anne Wexler applaud President Carter after his human rights speech. By Frank Johnston-The Washington Post