The first meeting between Ronald Reagan and Mikhail Gorbachev, at Geneva, became known as the "Firelight Summit." The second, at Reykjavik, was Heartbreak Hill. The third, which is sunlit with promise, may go down as the "Whatever Summit" -- whatever being what Gorbachev says he will do to end the arms race that is breaking his budget and Reagan's.

The treaty that the two men signed in the East Room merely will eliminate 4 percent of the superpowers' crammed nuclear arsenals. The event generated a general joy, even in the jaded Capitol, because here and in Moscow, onlookers thought they were witnessing the signing of a no-fault treaty to end the Cold War.

Gorbachev has, from the moment he landed, acted like a man possessed. He has come, he keeps saying, with a bargain we can't refuse. This is a pit-stop on the fast track that leads to reducing the world's nuclear terror, the halving of the intercontinental ballistic missiles, which could pulverize the cities of both countries.

For Gorbachev, self-confident as he is, the trip represents his chance to solidify his precarious position as leader of a people whom he is trying to drag into perestroika. He cannot go home empty-handed. For him, it's a matter of survival; for his host, resurrection.

Gorbachev is captain of a large team that is peddling the party line to every American it can collar. At briefings in the depths of the summit press center at the Marriott Hotel, Soviet spokesmen, who have been shorn of their bristles and speak with Oxford-tinged accents, tell of their eagerness to satisfy U.S. customer complaints.

Worried about the imbalance between Soviet and allied strength in Europe? "We are ready to address the problem of the disparities and asymmetries of our conventional forces," said Andrei Grachev of the Central Committee.

As for Afghanistan, the word is out. For prisoners of conscience, out, too. Jewish refuseniks? That's trickier, but if we are willing to give them a break on trade, everything is possible.

The ink on the treaty was hardly dry when experts from both sides were escorted into the press room to ratify its realities. The warmth of the occasion was still in the room, and the Soviets fell to looking beyond it.

The chief Soviet negotiator, Alexei Obukhov, who looks like a midwestern small-town banker, with a little tuft of white hair standing straight up, was asked about the INF verification standards, which, although the strictest ever written into a treaty, are not considered adequate by the United States for the strategic arms accord yet to be negotiated. No problem.

Said Obukhov equably, "If more verification is needed, then it will be agreed upon."

Gorbachev, in his rounds within the narrow confines of the Soviet Embassy and the White House two blocks away, was busy demonstrating to Reagan that he is a far tougher costar than Errol Flynn, whom the president facetiously cited as proof that he can hold his own against a heavyweight.

The Soviet leader seems to be stealing the president's lines in his drive toward disarmament, trade, acceptance, an end to ruinous rivalry.

He invoked God at the airport upon his arrival. Secretary of State George P. Shultz said, after Gorbachev's formal remarks, "That was a good start." Gorbachev answered, "The visit has begun, so let us hope. May God help us." The invocation of the Almighty by the leader of an atheist state was the first sign of Gorbachev's "whatever it takes" strategy.

In the afternoon, at a Soviet Embassy meeting of intellectuals, sprinkled with stars, Gorbachev borrowed another Reagan ploy. He held up a letter from a U.S. teen-ager named Emily Holden. She was urging the leaders to remember they are dealing with human lives. "Something very serious {is} afoot, something very profound," said Gorbachev, recalling the first-term Reagan who was always reaching out for humble correspondents who supported his tax cuts when Congress was resisting.

Gorbachev does not hesitate to speak for all mankind or, despite his country's history of repression, as a humanist. His speeches have considerably more reach than Reagan's. The president is providing all the cordiality and quips that are called for. But he is treading unfamiliar ground, as the host of a communist from a country he has spent his life deploring. He is up against an importunate, intellectual Bolshevik, with snapping eyes and a voracious thirst for encounters with the press, an institution that the president and the First Lady think is better held at arms' length.

Gorbachev knows just what he wants. Reagan is unsure, although he must suspect that what he is doing represents his last best hope for Mount Rushmore.