Additional undercover officers will be deployed to scrutinize the thousands of demonstrators expected to clamor for the attention of Soviet and U.S. leaders during the summit this week, according to a U.S. Park Police commander.

The "intelligence officers" will come from the U.S. Park Police, one of more than a half-dozen law enforcement agencies providing protection for Soviet President Mikhail Gorbachev during his five-day stay in Washington.

The mission of the extra officers is to prevent violence among the various groups of demonstrators and ensure that no violence is directed toward the Soviet visitors, Maj. Carl Holmberg said yesterday.

"We have them at every demonstration," said Holmberg, commander of the Park Police Special Forces Branch, "but we will add more this week. There are 18 different groups who have permits {to demonstrate}. We're paying more attention to them . . . . We try to analyze what their intentions are."

That is one of the small differences -- that anyone knowledgeable will talk about -- between the security preparations for this week's summit and those for the Reagan-Gorbachev talks in December 1987.

In Gorbachev's last visit, his movements were confined mostly to an area bounded by 22nd Street on the west and his embassy on 16th Street on the east.

This time, according to his announced schedule, Gorbachev will see not only more places in Washington but also more of the United States.

There is a possibility that he will accompany his wife, Raisa, on a visit to the Library of Congress. There is a day-long meeting with President Bush on Saturday at Camp David in Western Maryland.

There is a flight to Minnesota, where Gorbachev will see parts of three cities. And there is his final scheduled stop in northern California, where the Soviet president will dine in San Francisco and give a speech at Stanford University in Palo Alto.

All of that makes the security job tougher.

"It's bigger, logistically, to coordinate all of the press, all of the agents, all of the staff so things run smoothly," said Allan Kramer, a Secret Service spokesman. "But security is our business. That won't be as difficult as coordinating all of the people."

Gorbachev's plane is scheduled to leave Ottawa this afternoon.

A team of Russian-speaking U.S. Air Force escort pilots, called "shotgun pilots," will board the Soviet jetliners in Ottawa to help translate and read navigational maps, according to Air Force spokesmen.

If the planes take the most direct route from Ottawa, a controller at the Air Route Traffic Control Center in Nashua, N.H., will be the first on-the-ground aviation official to see Gorbachev's convoy on his screen, said Federal Aviation Administration spokesman Fred Farrar.

Secret Service officials declined to comment about whether Gorbachev's plane will have air escorts, but an FAA official said there would be none. Commercial traffic should not be a problem because Gorbachev's plane, like President Bush's Air Force One, flies at a much higher altitude than commercial airliners.

Gorbachev's plane is scheduled to land at Andrews Air Force Base in Prince George's County at 6:30 p.m. Before the landing, members of the county police's emergency services team will scour wooded areas and patrol by car and foot residential areas along Suitland Parkway, the likely route a motorcade would take into Washington.

Traffic around the base and along the motorcade route will be brought to a standstill, with local police using patrol cars to block intersections.

The same routine will occur every time Gorbachev goes anywhere by car.

In the District, police will close 16th Street NW between L and M streets from this morning until Sunday. Manhole covers around the Soviet Embassy and the Madison and Vista hotels have been sealed. Pedestrian access to that block will be limited, depending on Gorbachev's arrival at or departure from the Soviet Embassy.

The dozens of journalists entering a structure erected on the Ellipse for broadcasters will be subject to sweeps by bomb-sniffing dogs and will have to pass through metal detectors to get inside.

Background checks have been conducted on doctors and staff members at several hospitals who might be called upon in an emergency. Secret Service agents also have checked the records of the staff at the Madison Hotel, where a large parts of the Soviet summit delegation will stay.

The Secret Service and the KGB take primary responsibility for safeguarding Gorbachev in the United States.

"You're fine-tuning your plans, constantly updating," said the Secret Service's Kramer. "We check and recheck everything from the moment he steps off that plane to the moment he takes off to go back to the Soviet Union."

And all of the agencies, including the KGB, cooperate in the process. At one of the dozens of meetings to plan for summit security, KGB officials asked that temporary fencing be constructed near a demonstration site where U.S. officials had planned to use rope. A red snow fence will be in place.

"We plan for any eventuality and must be willing to throw everything out," D.C. Police Chief Isaac Fulwood Jr. said. "It is important to make sure that nothing happens that would embarrass us."

The Secret Service's preference is that nothing be left to chance, even though Gorbachev jolted those carefully thought-out plans during the 1987 summit when he unexpectedly got out of his armored Zil limousine and shook hands and waved to an afternoon crowd at Connecticut Avenue and L Street NW.

"That upset a lot of people," said a source familiar with security preparations for the 1987 summit. "But what are you going to do, tell him to stay in the car, that he can't do it?"

This time, officials said, they won't be as surprised.

"If he wants to stop the motorcade, we have no problem," Kramer said. "If anybody wants to wish him ill, they wouldn't know about it any more in advance than we would."