Two weeks before the Washington superpower summit, Soviet negotiators sent U.S. counterparts seated across the table in Moscow an unmistakable message: we are back to our old iron-pants ways.

That signal was sent Wednesday evening, May 16. Their opening session of presummit talks, starting at 5 p.m., had droned on for four hours with Foreign Minister Eduard Shevardnadze describing Soviet arms control positions. Secretary of State James A. Baker III, heading a jet-lagged American delegation, asked to adjourn for the night. Shevardnadze bluntly refused, asserting he had much more to say. The camaraderie displayed last fall in Wyoming between Baker and Shevardnadze was gone. The meeting droned on for another two hours, past 11 p.m.

As viewed by the U.S. side, the Soviets had returned to the negotiating style perfected through a half-century of handling Americans. The technique is all too familiar: rudeness, stubbornness and a pattern of rearguing issues that were seemingly settled. From Stalin-Roosevelt to Brezhnev-Carter, that technique had often delivered to Moscow more than Washington dreamed could be taken away.

The hard-nosed May 16 session set the tone for the rest of the Moscow talks, with the widely reported switch on Tacit Rainbow, the new U.S. air-launched cruise missile, the clearest reversion to Soviet form. But the Soviet negotiators' rejection of Mikhail Gorbachev's deal with Baker on Tacit Rainbow was only one sign of the return to old-style tactics.

Indeed, it seemed that in various ways the military was flashing signals to the U.S. side that it just does not like arms control. Instead, the generals want what one American negotiator called ''complete flexibility on all military matters,'' which means the ability to make the decisions, whether dealing with Shevardnadze or negotiating with Baker.

Soviet reversion to form was so abrupt that it raised speculation inside the Bush administration that iron-pants Soviet diplomacy made famous by Molotov and continued by Gromyko will persist into this week's Washington summit.

A completed START treaty is not ready for signing, and conventional arms talks are stalled. Meetings between President Bush and President Gorbachev are expected to concentrate on Germany and the Baltics; it will not be easy, judging from the tone at Moscow.

The mood change cannot be separated from the more obtrusive role of the Soviet military officers, including the sudden appearance at the Moscow talks of Col. Gen. Branislav Omelichev, deputy chief of the general staff. Seated at Shevardnadze's side, he presented an image of immobility. At one point when a question was asked by the Americans, Omelichev snapped ''no'' before the foreign minister could reply.

U.S. intelligence analysts cannot agree about the state of relations between the military and Gorbachev. But whoever is really in the driver's seat, there is little doubt about what caused the change in driving style. With the Eastern European empire gone, the Soviet Union itself disintegrating and its economy in shambles, the Kremlin has returned to time-tested caution in protecting the military and political balance of power.

That phenomenon causes thoughtful U.S. officials to reflect on differences in negotiating style between the two superpowers. Looking at the experience in Moscow two weeks ago, one such American told us: ''I don't think it's so much that the Soviets are better negotiators than we are. It's just that they're much ruder.''

It is a familiar contrast. On one side are Soviet officials, fearful that the slightest error will cast them into oblivion. On the other side are Americans laboring under no such inhibitions and eager for agreement. As with his predecessors, negotiator Baker wanted to reach his bottom line -- an objective not on the visible Soviet agenda.

Gorbachev in Moscow was confident, even arrogant, in demonstrating his mastery of details in one-on-ones with Baker. Reports of his impending demise are greatly exaggerated, or else he is ignoring it. While facing deepening crisis at home, the Soviet leader can be expected this week to combine self-assurance with that old-time Bolshevik obnoxiousness.