MOSCOW, NOV. 25 -- When the last meeting between Mikhail Gorbachev and Ronald Reagan came to the brink of collapse in Reykjavik, Iceland, 13 months ago, Marshal Sergei Akhromeyev took the lead in salvaging it, sparring with American officials through a long night of negotiations.

On the eve of the third summit between the two leaders, set to begin in Washington on Dec. 8, the career Soviet Army marshal and chief of the general staff has emerged once again as perhaps the Kremlin's most skillful negotiator, helping to pull both sides over last-minute hurdles in talks for a treaty to eliminate medium- and shorter-range missiles.

When the treaty was concluded yesterday in Geneva, it was Akhromeyev who drew praise from both sides as a decisive and indispensable spirit behind the first major arms deal completed between the United States and the Soviet Union in eight years.

Soviet Foreign Minister Eduard Shevardnadze, who led the Soviet delegation through its latest round in Geneva, called Akhromeyev "the most peaceful chief of general staff in the world." Praise from western officials also was glowing. "It is Akhromeyev," said one U.S. official in Moscow, "who has made the Soviet Union's professed interest in concluding agreements credible."

"When he shows up, we know we are going to get somewhere," said a U.S. official in Brussels who has been in negotiations with -- and without -- Akhromeyev.

The fact that the 64-year-old officer took part in the negotiations at all -- and is included as a senior member of Gorbachev's delegation for the upcoming Washington summit -- has struck arms specialists here as the strongest indication of an important change in the Soviet military leadership's approach to arms control.

Marshal Nikolai Ogarkov, who preceded Akhromeyev as chief of staff and deputy defense minister, publicly advocated increasing investments in Soviet defense spending to match western advances in new military technologies.

Ogarkov and an earlier generation of military leaders ushered through the deployment of hundreds of Soviet SS20 intermediate-range missiles in the Soviet Union -- a decision that has recently been described as a "political mistake" by a top Soviet Foreign Ministry official -- and the intervention of Soviet troops in Afghanistan, something that is also now controversial here.

It was during Ogarkov's tenure that Soviet forces shot down a Korean Air Lines jetliner in 1983.

In the view of western diplomats in Moscow, today's military leaders -- including Akhromeyev and new Defense Minister Dmitri Yazov -- take a more hard-nosed account of strategic decisions, weighing gains against economic and political costs.

Akhromeyev, however, is far from a dove on strategic issues. When Gorbachev returned to Moscow after failing to conclude a strategic agreement with Reagan at their first summit in Geneva in 1985, Akhromeyev publicly criticized the meeting in a speech before the Supreme Soviet.

In an attack on Reagan's Strategic Defense Initiative, published here in May, Akhromeyev charged the U.S. administration with seeking to to achieve military superiority over the Soviet Union.

Rather than viewing him as a dove, western analysts in Moscow see Akhromeyev as personifying a commitment at the top of the Soviet military leadership to avoiding costly defense expenditures wherever possible.

Under Gorbachev, Akhromeyev has emerged as not only a skillful negotiator but a spokesman on strategic issues. Although his thin, professorial visage is unfamiliar in the United States, Akhromeyev is well known to journalists here. He appears at important press conferences to defend some of the Soviet leadership's arms control policies, especially when they can be controversial within the military -- such as the decision to continue a unilateral nuclear test ban for 19 months.

According to some Soviet and western experts, Akhromeyev's main role probably is behind the scenes, however. During the Reykjavik negotiations, he consistently made on-the-spot decisions to keep the all-night talks moving, according to several U.S. officials who took part.

"His role in the arms talks and press appearances is that of an inside player, not that of a figurehead," one western diplomat said.

As the latest U.S.-Soviet discussions have entered their most crucial stage, Akhromeyev has attracted most attention as a new-style Soviet negotiator. When Gorbachev introduced new strategic arms proposals during an Oct. 23 meeting at the Kremlin with Secretary of State George P. Shultz, Akhromeyev sat in on the talks.

Akhromeyev, who apparently is the senior military official in charge of international strategic issues, draws heavily from his early training under some of his country's best-known military strategists.

After joining the Army in 1940, he worked his way up the ranks, serving as first deputy commander of the Far Eastern military division in 1974.

He then was transferred to Moscow, where he was appointed deputy chief of the general staff under Viktor Kulikov, now head of Warsaw Pact forces.

When Ogarkov took over the general staff, Akhromeyev worked under his tutelage. And when Ogarkov was ousted in September 1984, Akhromeyev was appointed to succeed him.