He already helps run one of the superpower governments in the world, but later this year White House Chief of Staff John H. Sununu will get a crack at another.

In a summer of movie sequels, this one might be called "Mr. Sununu Goes to Moscow." But this plot has a different twist.

Sununu is no wide-eyed outlander going to the capital to fight for justice and righteousness. He is an engineer and former state chief executive heading toward the former symbol of the Evil Empire to offer a new Soviet president some advice on how to make his government work.

If nothing else, Sununu's mission to Moscow is a measure of how dramatically the relationship between the two nations has changed. "It came out of the summit," said Steve Hart, deputy White House press secretary. Soviet President Mikhail Gorbachev "expressed an interest during the summit in how the presidency works in the United States."

Although Gorbachev has been in power for five years, he has only been president for a few months and he is still trying to set up the office. So the Soviets are less interested in learning about the exercise of power than in such everyday problems as the flow of paper and the relationship between a president and a legislative body.

The militaries of the two countries have had a number of exchanges of top-level officials, part of an effort to lessen tensions between the two longtime adversaries. But this marks the first time that the office of the presidency is involved in such an intimate way.

A small Soviet delegation spent Monday and Tuesday working in and around the White House, observing how the place works. The delegation was headed by Mikhail Shkabardnya, business manager of the Soviet Council of Ministers, which is akin to the U.S. president's Cabinet. Also joining a number of the meetings was Alexander A. Bessmertnykh, the new Soviet ambassador.

The group toured the White House facilities and met with officials in charge of Cabinet affairs, congressional affairs, communications, economic and domestic policy development and the White House staff secretariat. However, they were not allowed to see the Situation Room, where high-level decision-making is made during an international crisis. The Soviets also visited the Departments of Justice, Treasury and Agriculture.

The Soviets' schedule was put together by Sununu's office with an eye toward giving the visitors a broad sense of how the American presidency operates, with emphasis on such things as how federal agencies send their ideas to the president and how he consults them; how policy options are prepared for the president's consideration; how speeches are prepared; how the White House consults with outside groups; and how paper flows to and from the president.

Now Shkabardnya has invited Sununu to come to Moscow to look at the organization of the office of the presidency there and suggest ways to make it more efficient. Details of the trip have not yet been arranged.

"Everybody's got a real positive attitude," Hart said, calling the exchange of advisers "a measure of the nature of the relationship that's developed between President Bush and President Gorbachev."

Will the brusque American chief of staff also look for ways to spruce up his own operation? Sununu is "always open to improvements," said White House press secretary Marlin Fitzwater.