But what of the broader issue of NATO expansion?

Mr. Matlock said the Russians have a point when they say Mr. Gorbachev received a blanket promise that NATO would not expand. Mr. Baker, he said, never formally retracted the pledge that NATO's ''jurisdiction'' would not extend eastward. The arrangements on Germany were simply an exception to a more general rule.

Mr. Baker adamantly rejects this view. He said he never intended to rule out the admission of new NATO members. The proposal on NATO jurisdiction had applied only to territory of the former East Germany, the German Democratic Republic, and had been speedily withdrawn.

''I got off the word 'jurisdiction' very quickly,'' Mr. Baker said in a telephone interview. ''I do not recall using it with the Soviets. But let's assume I did use it once or twice. We quickly walked away from it. What defeats this whole argument is that we then insisted on the G.D.R. being in NATO, thereby moving NATO eastward.''

Mr. Zelikow sides with Mr. Baker. He says the United States went over the revised proposal on several later occasions and the Russians never complained. The diplomatic record also shows that the two sides never discussed the possibility of Poland, Hungary or other Central European nations joining NATO. If the Soviets took Mr. Baker's pledge as ruling out the alliance's expansion, they failed to nail it down.

''No Soviet ever said, 'NATO may extend to East Germany but no farther,' '' Mr. Zelikow added.

An Act of Compromise

The allegations of broken promises have colored the negotiations for a new NATO-Russia accord. Not wanting to give the Russians a veto over NATO policy, the United States took the position that the agreement should be a non-binding ''charter.'' Eager to pin the West down, the Russians insisted on a formal, legal ''agreement.''

The compromise was the Founding Act, a legally non-binding agreement at the highest political level. It records the alliance's assurances not to deploy nuclear weapons or ''substantial'' numbers of foreign troops on the territory of its new members.