Instructed to ask Marshal Mikhail Moiseyev last month why his Soviet general staff was blocking troop reductions imposed by the Conventional Forces Europe treaty, Ambassador Jack Matlock was told that because the Foreign Ministry, then headed by Eduard Shevardnadze, had negotiated it, the treaty had no standing with the military.

The chief of staff's claim to be exempt from solemn agreements made by the Soviet government stunned the Bush administration. It revealed for the first time how far President Mikhail Gorbachev's reform regime had fallen. Days later, dropping a second shoe, the marshal had his strategic arms negotiators repudiate a major part of the START treaty all but agreed to by Shevardnadze and Secretary of State James A. Baker III in Houston.

Those two shockers were key factors in Shevardnadze's dramatic Dec. 20 resignation and President Bush's first-ever decision Monday to "postpone" a summit with Gorbachev. The summit was scheduled for Feb. 11 in Moscow. As Bush said, he did not want to absent himself from Washington during the Gulf war, and he was disturbed by the Baltic crackdown. But equally important was his outrage at the Soviet military's new power to tear up key elements of the two arms control agreements.

Marshal Moiseyev's decision to tell it bluntly to Jack Matlock came a few days before Boris Pugo, minister of interior and head of the secret police, and Defense Minister Dmitri Yazov issued their forbidding law-and-order mandate. Order No. 493/513, made public only last week, authorized army-police patrols "armed with shooting weapons to be assigned to patrol in any case where the operative situation is tense, including 24-hour patrols when there are mass events by citizens."

Soviet specialists here are convinced that Shevardnadze had seen this order before he resigned with his warning against a new "dictatorship." Indeed, a desperate effort to derail the secret police and the military may have been his last act of political war against the hard-line forces of repression that were stripping reformers of their control of events -- almost certainly with Gorbachev's connivance.

Moiseyev is expected to take over as defense minister from the colorless Yazov in the near future. The promotion is likely to give the military its strongest hand within the Soviet government in several years. Moiseyev leads the rising group of senior officers who believe that Gorbachev, acting through now-departed leaders of the reform movement such as Shevardnadze, went much too far in pursuing glasnost and perestroika and in risking the breakup of the union.

They want emancipation from reform, and they want to end the military retrenchment that was in such favor during the first Gorbachev era. That rules out many of the arms control deals Baker and Shevardnadze cut between themselves and then sold to their bosses, Bush and Gorbachev. Moreover, the military hates Shevardnadze for his attack on its costly campaign in Afghanistan and for his public statement that the construction of the big radar at Krasnoyarsk was a violation of the SALT I anti-ballistic missile treaty.

Even though aware of the military hostility toward Shevardnadze, American officials were shocked when they got word that Moiseyev had acquired enough raw power to ignore two major arms treaties. Both were products of the brief era of reform and Soviet retreat from Eastern Europe that dominated Gorbachev's earlier period.

On the conventional arms treaty, Moiseyev has thrown out one agreement after another. The military "data base" that is supposed to reveal the full extent of Soviet tanks, armored vehicles, guns, non-nuclear missiles and troops has been systematically skewed so badly that it became a bad joke in the Pentagon. A sour example: two Army divisions assigned to the Navy as coastal protection forces, therefore (claimed the military) not covered by Conventional Forces Europe limitations on ground forces.

On the strategic-weapons START treaty, Soviet generals are known to feel terror about U.S. technological supremacy, particularly in the area of air-launched cruise missiles. That triggered the military's sudden refusal to accept Shevardnadze's agreements to exempt the B-1 and B-2 bombers from inspection.

Administration sources say privately that it may be a long time before Washington and Moscow come back to the negotiating table on either of these treaties with any chance of success. They are now disembodied and will probably remain so as long as Gorbachev's tenure depends on the support of his new friends, the generals.