President Carter's decision to withdraw American ground troops from South Korea was contributed to instability in Asia and the pullout should be slowed, according to a congressional report released yesterday.

It accused President Carter of failing to consider all factors before announcing the withdrawal and of consulting with U.S. military chiefs only after the decision had been made.

The report was drafted by a subcommittee of the House Armed Services Committee before Carter's announcement last Friday that he was delaying the withdrawal of two battalions, totaling 1,600 men, until the end of 1979.

"In the opinion of the subcommittee, the public announcement of this withdrawal . . . has already contributed to instability in Asia, has damaged our cooperative defensive relationship with Korea and has had a measurable impact on our relations with our other Pacific allies," the report said.

The subcommittee said no amount of U.S. reiteration of a conitinuing defense commitment could offset the damage a withdrawal would do.

It described the role of the 30,000 Americans stationed south of the Demilitarized Zone between North and South Korea as identical to that of some of the American forces in Europe - that of acting as a deterrent to attack in "the most explosive and volatile spot in Asia."

"Withdrawal of these troops will greatly impair the deterrent with almost no discernable gain," the report said. "With the world already faced with serious securtiy problem . . . America can ill afford to run the risks othat a preset timetable for withdrawal of American troops would entail."

The panel said withdrawal of any of the 30,000 troops without the concurrent transfer of equipment to the South Koreans would endanger the remaining Americans and increases the risk of war.

The Carter administration has proposed transferring $800 million in equipment to South Korea as partial compensation for the planned pullout. But congressional approval of the transfer is being held up because of the Korean influence-buying scandal.

The subcommittee said it did not oppose the initial withdrawal of 6,000 men subject to the transfer of equipment and other conditions.