A Pentagon task force has concluded that South Korea may need as much as $8 billion in additional military equipment to offset the withdrawal of American troops.

Administration officials stressed yesterday that President Carter has not committed himself to any specific amount of arms and that the $8 billion was "an outside estimate."

However, the Pentagon study serves notice that Carter's plan to withdraw about 33,000 troops over the next five years will cost a lot of money in additional weaponry.

Administration officials said South korea will be expected to buy most of the extra arms rather than receive them free from the United States. But this is expected to be argued when Defense Secretary Harold Brown talks with South Korean officials in Seoul later this week.

Brown is scheduled to leave for Korea on Friday.

The Pentagon task force in assessing what South Korea would need, listed about 250 jet fighters, including 90 of the F-16s now coming off production lines, plus hundreds of helicopters and observation planes, six destroyers and an assortment of missiles and guns.

Gen. George S. Brown, chairman of the Joint Chiefs of Staff, told a House Armed Services subcommittee last week that the chiefs went along with Carter's withdrawal plan only after being assured that South Korea's military would be beefed up.

Besides leaving behind much of the military equipment now in the hands of U.S. troops in Korea. Brown said he expected the administration would make it easy for the Seoul government to buy additional weapons.

The U.S. Army weapons expected to be left behind when American troops pull out include the Honest John rocket, which could be fitted with a nuclear as well as conventional warhead, although the United States is not expected to leave any nuclear weapons behind.

Some members of Congress would object to leaving any nuclear-capable rockets with the South Koreans for fear they would build nuclear warheads.

For the longer term, the Pentagon task force suggested that the United States help SOuth Korea expand its armaments industry, including plants for building tanks and helicopters.

Congress would have to approve sending additional weapons to South Korea to offset the American withdrawal. Carter is expected to outline what he has in mind, in meetings with Senators and representatives this week.

The precise list of weapons will not be decided upon, administration officials indicated yesterday, until after Brown returns from his talks with South Korean officials.

The Joint Chiefs had recommended a smaller withdrawal than the one Carter has announced, but have since said the complete withdrawal is "an acceptable risk," largely because of the President's pledge to send South Korea more weaponry.

The Joint Chief's reluctance is already bringing charges from several lawmakers, including Chairman Samuel S. Stratton (D-N.Y.) of the House Armed Services Investigations Subcommittee, that Carter's withdrawal plan may be military unsound.

Further complicating the administration's withdrawal plan and forthcoming requests to send modern weaponry to South Korea are the ongoing investigations into South Korean pay ffs to present and former members of Congress.

Administration officials fear that politicians may wish to disassociate themselves from approving special aid to South Korea to avoid suspicion they are returning favors.