President Park Chung Hee told U.S. officials today that he has reluctantly accepted the American plan to withdraw all U.S. ground troops from South Korea over the next four to five years but said the country will need American assistance in replacing them.

Under Secretary of State Philip Habib and Gen. George S. Brown, chairman of the Joint Chiefs of Staff, discussed the planned troop pullout with Park at a three-hour meeting in the Blue House, the South Korean president's official residence.

South Korean and Western sources described the closed-door consultation session as constructive, very frank and friendly.

Carter's envoys received a sober but not resentful hearing, the sources indicated, despite South Korean opposition to the withdrawal.

The American side reaffirmed a determination to fulfill its treaty commitment to the defense of South Korea faithfully. In the oft-repeated formula, the phasedown would be managed in a careful, gradual way so as not to destroy the military balance of forces on the Korean Peninsula or tempt a North Korean attack.

The U.S. officials undertook to help upgrade the South Korean forces, but gave no clue as to how this will be done, other than retaining U.S. Air Force units in South Korea, or at what cost.

At present there are 40,000 U.S. troops in South Korea, and 33,000 would be withdrawn over the four- to five-year period.

Park has previously stated he does not understand why the U.S. wants to phase out its ground forces in South Korea. Paling tribute to the contribution of the GIs in throwing back North Korean aggression in the 1950-1953 Korean War and in maintaining the stability of Northeast Asia for the last 24 years, Park made it clear today if the choice were his the troops would stay.

The Korean government accepted, however, the stated U.S. intention to take out American troops and wanted to move on to consideration of increasing the country's defensive strength as the withdrawal progresses.

During the withdrawal period the Park government plans to concentrate on making its military forces self-reliant, with American assistance, the sources said.

The American delegation said it hopes to gain a fuller understanding of South Korea's perceived needs in meetings with South Korea foreign and defense ministers scheduled for Thursday.

The talks are portrayed as consultations, but the decision to remove the troops within five years was given to the South Koreans as a flat, non-negotiable U.S. intent. The two countries are now starting to compare their respective estimations of what is needed to improve the South Korean forces and maintain the balance of power. It is not yet clear how long that will take, or whether there will be any substantial difficulties in reaching agreement.

The sources said that the subject of human-rights violations by the South Korean government did not arise today. But after leaving the Blue House, Habib met at the American ambassador's residence with Kim Wwan Suk, secretary general of the Korean National Council of Churches and a leading human-right campaigner. Kim said later: "I think something was accomplished. I think the meeting itself is very meaningful. It comes at a critical and sensitive time in Korea."