The South Korean ruling party's presidential candidate yesterday endorsed a future change in U.S.-Korean military command arrangements in the divided peninsula to give South Korea more control over its own military forces.

Roh Tae Woo, a former general whose call for direct presidential elections and other reforms stunned his nation June 29 and changed the political situation overnight, made the statement to Washington Post editors and reporters on the first day of a controversial preelection trip to the United States.

"It is natural for any sovereign country to exercise operational control over its own military forces," said Roh. "In the future, we should make efforts to see that things go in that direction . . . . Eventually the command structure will be changed."

A U.S. general has commanded the forces defending South Korea since the 1950-53 Korean war, a sore point with many Koreans in an era when Korea has 540,000 troops on duty and the United States only 40,000. Since 1978, a Combined Forces Command under the ranking U.S. general, with a Korean general as his deputy, has had operational control of all defending forces in Korea.

Last week the opposition Reunification Democratic Party pledged that if its presidential candidate is elected in the coming balloting, he would begin negotiations aimed at eliminating U.S. control over Korean military forces in the Combined Forces Command and "restoring independence in the operation of the Korean Army."

Roh was critical of the opposition platform, saying that politicians can say anything before elections and that "this is too serious for a campaign issue."

He went on to say that the delicate question of command relations should be handled cautiously because alteration of the military balance in the Korean peninsula could bring instability and increased danger of war. A change cannot be made "at this moment," said Roh, who went on to indicate his approval for an eventual shift.

The 54-year-old Roh, a longtime friend and associate of Korean President Chun Doo Hwan, began the day by meeting briefly with President Reagan, and later saw Secretary of State George P. Shultz and Undersecretary Michael H. Armacost. He also delivered an address to the Johns Hopkins School of Advanced International Studies.

Roh's trip has been criticized by the political opposition as an effort to win U.S. support for his presidential candidacy or to give the Korean people the impression of U.S. support.

State Department spokesman Charles E. Redman repeated yesterday that "the United States is not taking a position in any way on individual candidates. We made it very clear that what we support is the process that is under way in Korea, and that we would welcome visits by leaders of either camp." The opposition party has not yet named its presidential candidate.

Roh said at The Post that some members of his own Democratic Justice Party had questioned his timing in coming to Washington. He insisted he did not come out of partisan considerations, but to tell the U.S. government and people that "a political miracle is happening in Korea."

Shortly before leaving Seoul, Roh said, he met opposition party president Kim Young Sam at a reception and told him, "I am not going {to Washington} just to deliver my message; I'll deliver your message too."

Asked whether the Korean military would accept an opposition party president if Roh is defeated this fall, Roh called the Korean forces "a democratic military" and said that if the next president is elected by the people, he has "the firm conviction" that the military will honor that choice.

Roh, who in 1983 was president of the 1988 Seoul Olympics Organizing Committee, said South Korea should not offer further concessions in the negotiations over North Korean participation in the games. In the past South Korea offered to permit the North to host all or part of five events as an incentive for them to participate, but this was rejected by Pyongyang.

The invitations for the Seoul Olympics are to go out this Thursday, which has been considered a deadline for North Korea to agree to a partial hosting arrangement. Roh said a team from the International Olympics Committee had determined on a visit to Pyongyang that the North is "not capable" of handling the five events offered by the South. The North Korean demand for even more, he charged, is "an excuse" for a decision not to participate in the games.