Just as the wailing horns of the Soviet motorcade were heard in the distance, President Reagan stepped into the bracing cold winds off Lake Geneva without an overcoat and waited on the steps of the Swiss chateau for his first words with a leader of the Soviet Union.

When Mikhail Gorbachev climbed out of the black Zil limousine with a Soviet flag flying from the right fender and took off his charcoal-gray hat, the first conversation he had with Reagan was about the overcoat. Gorbachev gestured to his own coat and asked the president, in Russian, "Where is your coat?"

"It's inside," Reagan said, motioning toward the glass doors and warmth of the 120-year-old Swiss chateau, as they posed for photographers in a chill wind. The president steered his guest by the elbow inside, and so began an extraordinary personal encounter between the American president, who devoted a career to denigrating communism, and the Russian who may rule his Communist nation into the next century.

It was a meeting of historic significance that began in an air of nervous cordiality, a day planned months ago that was marked by unexpected last-minute twists, an encounter by the leaders of hostile superpowers that produced moments of gentle humor.

Whatever deep divisions were expressed in private, the first meeting between Reagan and a Soviet leader was wrapped in an air of outward friendliness and informality. Reagan was all smiles, and began the day by coming to a window and flashing a thumbs-up sign to reporters as he awaited Gorbachev's arrival at villa Fleur d'Eau.

Later, in a tiny, pale-blue sitting room, the two leaders waited edgily for their first dose of a contemporary ritual of the American presidency: the three-stage "photo opportunity." First, a wave of American reporters and photographers bustled in. Reagan and Gorbachev chatted about jet lag. Gorbachev, an interpreter at his side, told Reagan it took him two weeks to recover from a trip to Canada.

"It's better when you are going west," responded Reagan.

Then a question was thrown across the room from ABC's Sam Donaldson to Gorbachev.

"Mr. General Secretary, Andrei Gromkyo once said of you that you have a nice smile but iron teeth -- I guess meaning you're tough. What do you have to say about that, sir?"

"It hasn't yet been confirmed. As of now I'm still using my own teeth," Gorbachev responded, animated, in good humor, and shifting in his chair. "But as to the substance of your question, both the president and I have good grounds to believe we can have a good talk."

Reagan has been through hundreds of similar photo sessions, but today he seemed pensive and a little ill at ease as the questions continued. Asked his first impression of Gorbachev, he started to say they share the same goals.

But suddenly his words were drowned out by a jarring burst of static and voices from a television cameraman's walkie-talkie. Reagan seemed unsettled as the quarrelsome walkie-talkie would not be silent, barking out noisy commands.

The American reporters were ushered out. The Soviet reporters came in. They wished Gorbachev "good luck," and the Soviet leader suggested that they wish Reagan good luck. They did, according to S. Kondrashov of the Soviet newspaper Izvestia, who swapped notes afterward on the driveway with the Americans.

After smiling through another wave of Swiss journalists, Reagan and Gorbachev retired to a room at the rear of the villa for their first private conversation.

It was supposed to last 15 minutes, but as the meeting wore on, Soviet and U.S. officials fidgeted and paced in the large conference room at the front of the villa, where the formal meeting was to begin. They could be seen by reporters outside through wide glass doors.

It was a time of curious uncertainty. The summit had been choreographed down to the minute, yet in the first hour, it was not going according to plans. No one -- the pool of reporters outside, or the Soviet and American advisers inside -- knew what the two most powerful leaders on the globe had found to keep them talking alone for so long in their first encounter.

The two leaders came out an hour later for more photographs before the formal session with advisers. Reagan was beaming, but perfunctory.

"We were very businesslike," he said.

Among the U.S. and Soviet officials who waited in makeshift offices upstairs during the meetings was Ronald Prescott Reagan Jr., the president's son, who was spotted in a red flannel shirt amid the navy blue pinstripes.

"Are you ready, Dad?" he asked the president before Gorbachev arrived, according to Speakes.

"Absolutely," Reagan replied.

Then Ron Jr. suggested the president toss a football with Gorbachev out on the lawn. Speakes said Ron Jr. had asked to be present at the photo sessions to be a "witness to history," but as he rode in a van later with reporters, Ron Jr. said he had come here to write an article for Playboy magazine.

The afternoon brought more unexpected turns. After lunch, during which Gorbachev unexpectedly met with American peace activists at the Soviet mission and Reagan quietly secluded himself with senior advisers, Gorbachev returned to the villa in the Zil limousine.

"Did you have a good lunch?" Reagan asked, then guided the Soviet leader back inside, telling him "we don't have to stop" for photos.

Reagan and Gorbachev walked privately down to a large pool house by the lake after lunch, talking alone, except for interpreters, for 54 minutes before a blazing fireplace.

Tonight, Reagan and Gorbachev were talking with their wives before a dinner at the Soviet mission. Asked if the day had brought progress, Reagan said, "We're still smiling."