President-elect Jimmy Carter has told members of Congress that he will use his influence with South Korean President Park Chung Hee to ease political repression in that country, at the same time moving ahead with his plan to withdraw U.S. ground troops.

Carter's statements became known as he work closeted with the Joint Chiefs of Staff and his national security of military policy which ran several hours longer than originally scheduled. Carter aides said the lengthy meeting - which started at 8:30 a.m. and continued with brief interruptions until 6 p.m. - covered such matters as U.S. military deployments and the U.S. Soviet Strategic Arms Limitation Talks.

Planned meetings with civilian Pentagon officials about the military budget and proposed new weapons systems were canceled in order to continued the talks with the military chiefs. Press Secretary Jody Powell said the change was made because "the original estimate of time was unrealistic. There was a great deal of information to be exchanged."

After the meeting at Blair House, Carter was quoted as saying it was "frank, complete and very beneficial." Secretary of State-designate Cyrus R. Vance, who participated, told reporters that a new SALT agreement with Russia remains "a very high priority" of the incoming administration.

Secretary of Defense-designate Harold Brown and Deputy Secretary-designate Charles Duncan Jr., who also took part in the long session, won unanimous recommendations of confirmation during the day from the Senate Armed Services Committee.

Chairman John C. Stennis (D-Miss.) said the committee made "an outright exception" to its general rule in agreeing to permit Duncan to retain his $12 million in stock in Coca-Cola Co., which he once headed, despite the fact that the firm does business with the Defense Department. Stennis said the exception was made because the firm sells the military soft drinks rather than military hardware.

The Carter proposal to withdraw U.S. ground troops from South Korea wa announced during his campaign for the presidency. He reiterated his plans Wednesday during a day-long foreign policy discussion at the Smithsonian Institution attended by about 50 members of Congress as well as his national security team.

According to participants, the President-elect told lawmakers he had not made his campaign statements lightly, but only after very carefully considering the problem of U.S. troops. He added that the United States should continue air cover in South Korea and should make sure that the South Koreans have adequate troops of their own to defend themselves, the sources said.

The United States has about 40,000 troops in Korea compared to South Korean ground forces of 580,000 - the fifth largest army in the world. North Korea has about 410,000 ground troops.

Vance reported to the Smithsonian meeting that Japanese leaders are concerned about the planned U.S. withdrawal, but that they have been assured no action will be taken without consulting them. The withdrawal plan was reported to have been among the topics discussed in a telephone conversation Wednesday between Carter and Japanese Prime Minister Takeo Fukuda. Carter has also pledged to consult South Korea about his plan.

After a member of Congress at the Smithsonian meeting asked how the United States could maintain leverage on Park to ease "tyranny" in that country, Carter expressed his concern about human rights there and said he will seek to persuade Park to ease the situation, sources said. Internal political opposition to Park is suppressed under presidential decrees, and 18 leading Christian dissidents were recently sentenced to prison terms.

An official of the incoming administration reported that some people have proposed U.S. contacts with North Korea as part of the troop withdrawal process, sources said. The lawmakers and the Carter team discussed the possibility of a "two Korea" policy without any consensus, it was reported.

Carter interrupted his meetings with the Joint Chiefs of Staff to make telephone calls of 10 to 15 minutes each to President Valery Giscard d'Estaing of France and Prime Ministers Helmut Schmidt of West Germany and James Callaghan of Britain. There were few details of the conversation, but officials abroad described them as cordial and cooperative.