US negotiators well trained for Moscow talks. For rail buff Shultz, nothing could be finer than dinner in the diner

One of the President's arms control advisers played on a harmonica. The secretary of state watched the Finnish countryside roll by the window. And the national security adviser, standing in a corridor, off-handedly chatted about sublimits on nuclear warheads. For a brief time this week, one of the power centers of the United States shifted to a train rolling along the Gulf of Finland and into the Russian heartland.

On it were some of the highest-ranking US officials, accompanying Secretary of State George Shultz to Moscow for two days of discussions with Soviet officials that could pave the way to an arms control treaty and a superpower summit.

Mr. Shultz's plane could not land in the Soviet capital, which has been shrouded by fog for much of the week. But with both the Soviet Union and the US anxious to talk, the American entourage - with the help of the Finnish government - made its way to Moscow by means from another era: a five-coach train.

The train was hastily assembled by the Finnish State Railway when it became apparent the fog would not lift from Moscow in time for Shultz's scheduled arrival.

It was the first time in decades that a US secretary of state had journeyed to Moscow on train, and probably the first time in history that a train had crossed the heavily guarded Soviet border with so little attention to protocol or scrutiny.

``The whole thing went extremely smoothly,'' a diplomat said.

Soviet officials, at least, were anxious to use the journey as a metaphor for the hard bargaining ahead. Foreign Minister Eduard Shevardnadze, greeting Shultz in Moscow, observed, ``I think the obstacles that sometimes come up during the negotiations are insubstantial compared to the obstacles which you had to overcome to get from Helsinki to Moscow.'' To which the cautious Shultz replied, ``We'll see.''

The trip was not without hitches. At one stop, four uniformed border guards of the Soviet secret police did make a perfunctory attempt to enter the train's baggage car, where classified documents were sealed in a diplomatic pouch. They were politely but firmly turned away by US Marine security guards.

In fact, the Soviets had even expedited the issuance of visas to make sure those marines were on board. Americans took that as a sign of the high hopes that Moscow is pinning on the talks.

Shultz and National Security Adviser Frank Carlucci will be meeting not only with Mr. Shevardnadze, but also with Soviet leader Mikhail Gorbachev.

Shultz had another reason for being buoyed by the trip. Said one aide, ``He just likes trains.'' The secretary of state has a model railroad set up in his home in Palo Alto, Calif. The diplomatic cover story: It's for his grandchildren.

Mr. Carlucci, wearing a red, white, and blue sweater, strode about the train Wednesday night, stopped in a corridor, and reflected on the talks that awaited in Moscow. The Soviets ``want to put a big push'' on reductions in strategic arms, he said.

But Shultz observed that the Soviets have been telegraphing their punches through lower-level diplomats and journalists, not through official negotiating channels. The challenge for the US, said Shultz, is to ``have [the Soviets] say to us'' what they're saying unofficially elsewhere - namely, that most of the stumbling blocks to a treaty limiting intermediate-range nuclear forces are out of the way, and substantial progress can be reached on limiting long-range weapons.

Even as Carlucci and Shultz - two of the US's most senior national-security officials - were deep into Soviet territory, US officials said they were still able to communicate with the White House. But they weren't saying how this bit of technological wizardry was being accomplished from a moving train.

Another item that wasn't being talked about was equally ticklish: who would foot the bill for the unplanned train trip, especially with Congress assiduously paring back the US diplomatic budget.

``We don't know who's paying,'' said Shultz. ``The State Department,'' he said, ``is broke.''