President Reagan arrived today at this heavily secured historic site of the ninth economic summit of western leaders and declared that the world is recovering from "serious global recession" and now can address the problems of unemployment and protectionism.

"Recovery is what this summit is all about," Reagan said at Providence Hall soon after his arrival here this afternoon. "We're convinced that the growing convergence of domestic economic policy among the countries to be represented here will help sustain recovery and expand it to the rest of the world. With inflation increasingly under control, we can turn our collective attention to solving such problems as protectionism and unemployment."

Earlier, in an interview with eight reporters in the Oval Office of the White House, Reagan said he didn't foresee anything "of a confrontational nature" in the annual meeting of leaders of the United States, Britain, Canada, France, West Germany, Italy, and Japan.

But it still has attracted 3,000 accredited journalists to this community, which celebrates colonial America. Its period buildings have been laced with 25 miles of electronic cable to enable the leaders to transmit carefully orchestrated glimpses of their statesmanship to television viewers back home.

Present White House plans call for Reagan to be seen in formal and ceremonial settings designed to show him off as a world leader. The media will be kept at a distance, except for television cameras. White House advisers have made it clear that they do not want Reagan to give any impromptu answers to questions hurled at him by reporters.

American preparations for the first of these summits to be held in the continental United States have been extensive, expensive and well-organized. Official estimates of the cost range between $6 million and $8 million, but there are other built-in logistical and security expenses that may not be included in this figure.

For the first time since its Rockefeller-financed restoration was completed, most of Colonial Williamsburg has been closed to the public.

Summit personnel and the press are occupying nearly all of the 6,000 hotel rooms available in the Williamsburg area. They have been provided a variety of American-style food ranging from fried chicken and hotdogs to yogurt and ice cream cones, served late into the night in a gigantic powder blue-and-white tent covering eight tennis courts.

Reagan will spend his weekend in a beige clapboard house adjoining a well-manicured golf course, surrounded by huge magnolia and pine trees. An aide said the president had nothing on his schedule tonight.

Asked by reporters what he feared most here, the chief American summit organizer, Michael McMannus, said, "the unknown."

He said Italian Prime Minister Amintore Fanfani won't be able to see Jamestown, as he had wished, apparently because it is not within the area put under a tight security blanket. West German Chancellor Helmut Kohl will be served steak instead of what the other leaders will be eating at one meal, according to McMannus, because he won't eat the shellfish on the menu.

In his Oval Office interview before coming here, Reagan expressed his long-held view that optimism is a necessary ingredient of economic recovery both in the United States and other countries.

"I've always believed that there is a psychological factor in things of this kind," he said. "If you have people feeling pessimistic, you're going to have a holdback on investments."

Asked whether his thinking was changed by his extensive briefing for the summit, Reagan replied: "No, much of the extensive preparation is because, being the host, I'm going to be in charge. I'm going to be, you could call it moderator or whatever. And this has been a case of talking to the people that have been in the various meetings, all of the discussions that had been going on, so that I won't, in the series of meetings, overlook anything."

The president took a strong stand against protectionism in the interview, as he has in many statements.

"All of us are going to be on the side of not only resisting protectionism, but looking into where it presently exists, how much we can do to lessen it," Reagan said. "In fact, I found agreement among everyone that this is not the way to go, that the more we can go for a free trade the better off we will be."

Later, in his remarks on arriving here, Reagan noted the "magnitude of the problems that confront us" and the difficulty that high unemployment is causing in many countries, including the United States.

"With 22 million people unemployed in the seven summit countries, we must not flag in our efforts to ensure a recovery that is durable, non-inflationary and rooted in the democratic values that we as free people cherish," Reagan said.