Last month, flying over the blue-collar city of Manchester, N.H., President Reagan turned to Gov. John H. Sununu and told him:

"What I'd really like to do with Mikhail Gorbachev is to pick any house down there" and introduce the Soviet leader to the "working people" of the United States.

"I'd like to ask him to compare our way of life with that in the Soviet Union," Reagan said, according to a White House official who was with Reagan and Sununu in the presidential helicopter, Marine One.

The president's comments typify the kind of old-fashioned and uncomplicated approach Reagan is bringing to next month's summit meeting with Gorbachev, very possibly the most important diplomatic encounter of his presidency. Longtime associates and senior White House officials who are preparing Reagan for the event -- with papers, briefings, videotapes of Gorbachev speeches and possibly a mock summit -- have high expectations and deep concerns about his performance.

Reagan's strengths, they say, include his total self-confidence, his charm and his ability to rely on general principles that have been familiar to him for years.

But in a series of interviews the officials said Reagan still has little expertise in the details of nuclear weapons issues, and has sometimes made embarrassing mistakes, such as his misstatement of relative U.S.-Soviet military strength in his last nationally televised news conference. Another concern is that at the summit, Reagan might lapse into the harsh rhetoric of earlier years when he predicted the demise of the Soviet system, or preach to Gorbachev about the advantages of the American way of life.

"We have to fine-tune him rather than cram him," said a longtime Reagan associate who is helping with summit preparations.

The tutoring of Reagan is one of the most important aspects of White House preparations for the summit.

In the process, Reagan will make major policy decisions on issues from Afghanistan to the establishment of a superpower crisis center. Reagan will also oversee a "public diplomacy" campaign designed to put the U.S. stamp on world opinion before and after Geneva.

The fine-tuning has already started with 25 "foundation" papers, about a dozen of which have been sent so far to Reagan, outlining Soviet history, politics, foreign policy, society and culture.

Reagan will also consult with Soviet experts outside the government, conduct weekly National Security Council meetings, and perhaps stage an advance rehearsal of the nine hours of meetings scheduled for Nov. 19-20.

He may also consult with former presidents Richard M. Nixon, Gerald R. Ford and Jimmy Carter, all of whom met Soviet leaders during their terms. He will try to sharpen his major points with a speech to the United Nations, and an informal summit with western leaders, in New York later this month.

For the first two weeks of November, everything on Reagan's public and private schedule is being linked to the summit, and three days of total immersion in summit issues is planned just before Reagan departs Nov. 16 for Geneva, officials said.

One sign of the importance the president and Nancy Reagan attach to these preparations is the decision to bring three longtime advisers into the process: former deputy White House chief of staff Michael K. Deaver, pollster Richard B. Wirthlin and former White House speech writer and campaign adviser Kenneth L. Khachigian.

Overall responsibility for readying the president on "policy" matters rests with national security affairs adviser Robert C. McFarlane, in tandem with White House chief of staff Donald T. Regan, who handles "process," aides said.

Three White House groups are preparing for Geneva. One, comprised of mostly presidential aides, is co-chaired by McFarlane and Regan. Beneath it is an interagency group run by John F. Matlock Jr., a senior member of the NSC staff who handles European and Soviet affairs.

A third "advisory" group is headed by McFarlane's deputy, Vice Adm. John M. Poindexter, and Regan's deputy, Dennis Thomas. It handles the "public diplomacy" effort, which is a combination of public relations and attempts to shape U.S. and world opinion. Robert Korngold, a U.S. Information Agency official in London, has been brought to the White House to coordinate much of that effort.

While making many advance plans for Geneva, White House officials said they expect Reagan will also rely heavily on his instincts as an orator and negotiator. Several officials said they thought it would be an error to "overprogram" Reagan for the summit.

"Reagan being Reagan has pretty well got him squared away for this," a senior White House official asserted.

This official cited preparation for the visit of Soviet Foreign Minister Eduard Shevardnadze, for which Reagan received a 30-to-40-page briefing paper, with about 12 pages devoted to suggested "talking points" that Reagan later incorporated into his remarks. White House officials, including McFarlane, pronounced this "dry run" a success.

"It works for him," the senior White House official said. "He knows what he wants. I don't think he's going to be arguing SS18s and 19s with Gorbachev. He's going to be debating principles. He's anxious, he's feisty about it, he feels like he's got some good debating points. He feels that for the first time we've got the Soviets to lay numbers on the table and although we are far apart, we have some basis for talking."

Another top White House official said Reagan's Sept. 17 news conference, devoted largely to summit topics, illustrated how the White House would prepare by letting Reagan "use his own words." Reagan had a general discussion about the summit with aides beforehand, and then said, in response to a question about Gorbachev, "I wasn't going to give him a friendship ring or anything." Aides said they were pleased with his performance, particularly with that impromptu one-liner.

But the news conference also brought Reagan's incorrect statement that the United States is "still well behind the Soviet Union in literally every kind of offensive weapon, both conventional and in the strategic weapons," which even his most enthusiastic Defense Department backers acknowledge was hyperbole. He also discussed the Strategic Defense Initiative (SDI) in a way that led officials the next day to "clarify" what he meant.

Some officials and outside specialists say that Reagan needs exhaustive preparation on the specifics of nuclear weapons issues before the Geneva summit. One outside Soviet expert who has been consulted by the White House said Reagan "needs a great deal of education."

"If he talks to Gorbachev the way he talks to American reporters or even the way he talks to British Prime Minister Margaret Thatcher, there could be trouble," this specialist said.

These concerns have been echoed at the White House, where one insider recalled that the president's first debate performance last year with Democratic presidential nominee Walter F. Mondale was widely viewed as a disaster for the president. "The key thing is that in the arms area, he does not have expertise. One thing we observed after the Mondale debate was that Reagan had not debated for a long time. He was not at razor edge. Gorbachev is going to be sharp."

This official added that he was concerned even though "I always have great faith in the old man pulling through."

Yet another concern is that Reagan, who is expected to be sharply critical of the Soviets on human rights and a number of other issues, avoid some of the harsher rhetoric of earlier years, such as his description of the Soviets as a "focus of evil" or his predictions that communism would yield to a "freedom tide." According to Soviet officials, Reagan gave an anti-Soviet lecture last spring to Soviet politburo member Vladimir Shcherbitsky, who led a Soviet delegation on a visit to Washington.

In another episode, according to a source close to Nixon, the former president briefed Reagan thoroughly before his meeting last year with Andrei Gromyko, then the Soviet foreign minister. Nixon told Reagan, this source said, to be as businesslike as possible, and to avoid preaching to Gromyko. Later, the source said, Nixon learned that "Reagan completely ignored his advice."

Reagan has made a studied effort since January 1984 to mute his rhetoric, and McFarlane has emphasized repeatedly that Reagan accepts the Soviets as a superpower and does not seek to change their system.

Over the years, Reagan has given both brilliant and terrible performances as a result of skilled or flawed preparation by his staff.

Officials said they have learned some lessons from past attempts to prepare Reagan for debates, meeting foreign leaders and bargaining with political leaders at home.

One lesson is the importance of giving Reagan a solid dose of what to expect. An extensive effort is planned to anticipate what the Soviets will say in Geneva and to brief the president, probably just before he leaves, according to one planner.

Another lesson is that Reagan often learns more from actual contact with staff and experts, or from visual displays, than from briefing papers. He used full-dress rehearsals before presidential debates in 1980 and 1984, and they are standard procedure before every formal news conference.

When Reagan hosted the seven-nation economic summit at Williamsburg in 1983, a major rehearsal was held in advance with various aides and government officials standing in for the visiting heads of government, according to a participant.

In this case, Reagan will study videotapes of Gorbachev making speeches in the Soviet Union, officials said. A rehearsal of the Gorbachev meeting also is under consideration.

The State Department's Foreign Service Institute is preparing to videotape a day-long conference of Soviet experts to be held this week, and edited excerpts later may be shown to the president.

One White House official said a number of Soviet experts are to be brought in to see the president, but the final list of those to be invited has not been prepared. Reagan has already met with writer Suzanne Massie, a student of Russian culture. Massie told The New York Times after the meeting that Reagan "doesn't know anything about the Soviet people at all. He's in the same position as other Americans, despite all his advisers . . . . "