Playing host to an economic summit is a singular honor, many residents of Tokyo believe, but one that fortunately comes only once in seven years.

On Sunday afternoon, leaders of the noncommunist world's seven major industrialized nations will gather at the ornate Akasaka Palace here to begin three days of discussions on the world economy. Even before their arrival, they are paralyzing the core of this city of 8 million people.

For days now, police officers -- 15,000 of them at any given time -- have been sealing off side lanes, searching cars at checkpoints on busy thoroughfares, knocking on doors of apartments that overlook sensitive spots, climbing down manholes, sorting through contents of trash cans, frisking deliverymen.

Joggers have been shooed off the popular three-mile track that circles Emperor Hirohito's Imperial Palace. Merchants running shops in the two major hotels being taken over for the summit, the New Otani and Okura, have been encouraged to close down for the duration, leading some to demand government compensation.

Even the fish in the ancient Benkei Moat have not gone undisturbed in this single-minded quest for security. Navy divers have been groping around in the murky waters there for anything that might spell danger for the adjacent New Otani.

"With all the controls on traffic, we've lost our appetite for going out," lamented Yukiko Okazaki, a 25-year-old housewife. "They should not be holding the summit here. Why not in a more distant place?"

But authorities here viewed the central city as the only place with the proper mix of security and comfort. The Japanese excel at choreographing mass events of this sort and the preparations are proceeding smoothly. Altogether, about 12,000 people -- presidents, prime ministers, bureaucrats, journalists, waiters, telephone technicians -- will take part on the inside.

The influx of leaders began today, with the arrival of Italian Prime Minister Bettino Craxi. President Reagan comes Friday evening, with West German Chancellor Helmut Kohl and Canadian Prime Minister Brian Mulroney following Saturday. British Prime Minister Margaret Thatcher and France's dual leadership, President Francois Mitterrand and Prime Minister Jacques Chirac, show up Sunday.

Their host in the palace's cobbled courtyard Sunday afternoon will be Prime Minister Yasuhiro Nakasone, one of the few Tokyo residents who does not feel put out.

Modeled in miniature on France's Versailles, Akasaka Palace was completed in 1908, in the days when the newly opened Japan was wolfing down western culture. Originally a residence for the crown prince, it survived World War II and became a state guest house in 1974.

Plenary sessions will occur around a massive wooden table, used for the same pupose at the last Tokyo summit, in 1979. Overhead in the ballroom, decorated in the style of 18th-century France, are three chandeliers and a ceiling painted with a scene from the Japanese traditional play "Hagoromo" ("Robe of Heaven").

On Monday, Nakasone will lead his counterparts to a Japanese-style annex on the palace grounds and eat a Japanese meal at a low table. Seemingly, they will be sitting on the tatami mat floor but in fact a pit below the table will accommodate any stiff western legs.

Such a concentration of top leaders has made the government here fearful of attack, possibly by Libyans in retaliation for the U.S. air strikes on Tripoli and Benghazi last month. But so far, Libyans, of whom there were only 65 in Japan at the end of March, have made no showing.

Very visible, however, are extremist groups on the Japanese left, who have been firing homemade rockets at targets that include the Akasaka Palace, the U.S. Embassy, the Imperial Palace, a police headquarters in Osaka and a U.S. air base ouside Tokyo. They have also snarled commuter train movements by cutting communications cables.

In most cases, the attacks have caused noise and confusion, not injury or damage. The rockets are fired by timers from stolen cars or trucks parked near the targets. Police have succeeded only once in collaring a suspect on the scene.

Rooted in the radical student movement of the 1960s, the groups espouse Marxist revolution and claim major public support today. However, police and mainstream social commentators dismiss them as having at most several tens of thousands of supporters in a nation of 120 million people.

To the amazement of foreign visitors, the groups maintain public offices, flags and spokespersons. In their party newspapers, they proudly claim various attacks, sometimes printing diagrams of the rockets' trajectories.

The Middle Core Faction, best known of the groups, is headquartered in a fortified three-story pair of buildings in Tokyo's Ikebukoro district. Its front door resembles a bank vault's. Windows are barred and one building has a lookout tower complete with helmeted sentry.

"The summit is the summit of world war," said Katsumi Kanayama, who described himself as a ranking officer in the movement. "With all the power the Japanese people can muster, we are going to destroy it," he said.

Authorities here, sensitive to criticism that they are reviving the police state of World War II, tolerate political acts that in many other countries would be met with charges of conspiracy or national security violations. The police constantly search the radicals' buildings, question them and follow their cars, but to jail someone generally requires proof that he or she actually fired a rocket or cut a cable.

"This really makes the police frustrated," said Kanayama.

Police say they have arrested five top radicals since March and broken up arms-making shops. But in jail, members rarely give away their comrades. Japanese society values loyalty to the group. Members often turn over their salaries to the organization and allow it to direct their personal lives.

Some Japanese dismiss the groups as childish imitations of "real" guerrilla groups like the Palestine Liberation Organization or the Irish Republican Army. But Kanayama says they are dead serious and the police worry that next time they may use real weapons.

So police are taking no chances. For the occasion, the government has spent $40 million for new helicopters to ferry guests and another $40 million for new police equipment. Police reinforcements have been brought in from around the country -- one unit from Shikoku Island arrived with 20 vehicles, including a truck mounted with a water cannon. Some officers are reported to have sworn off drinking until the close of the summit.