President Reagan has arrived here in advance of a seven-nation economic summit meeting, but his spokesman quickly said that the administration would not be concerned if the economic issues here were overtaken by a discussion of the global issues raised by the Soviet nuclear accident and international terrorism.

"If they are, so be it," said White House spokesman Larry Speakes of the possible new emphasis at the meeting. "You've got seven world leaders here joined in face-to-face meetings and several hours of conversation, and you have something that is a danger to all nations such as the Soviet nuclear accident on the agenda. What better time to have them meeting than now, when the world is confronted with terrorism," he added.

While these events may overshadow the economic nature of the meeting, the leaders are gathering here in the most favorable economic environment in years.

The seven heads of government meeting here for three days beginning on Sunday originally designed this meeting as a celebration of global economic recovery. But the recent meteoric rise in value of the Japanese yen in world currency markets, especially against the U.S. dollar, has intruded on that celebration and now looms as the main and most contentious economic issue at this 12th economic summit.

Reagan was greeted last night by a host of Japanese dignitaries and U.S. Ambassador Mike Mansfield on his arrival from a three-day visit on the Indonesian resort island of Bali. But the extremely tight security here and the high tensions surrounding the Reagan visit because of recent terrorist activities were also quickly apparent. A group of reporters traveling on Reagan's plane were surrounded by Japanese police and forced to move away.

The meeting opens formally with a dinner Sunday night for the heads of the governments of the United States, Japan, West Germany, France, Great Britain, Canada and Italy.

To the extent that any economic issue can edge aside more pressing global problems such as the Soviet nuclear accident at Chernobyl and state-sponsored terrorism, the yen-dollar debate will dominate this heavily ceremonial annual event.

Two other major economic problems will get attention: farm trade and the rate of economic expansion in both Japan and Europe. Here, it will be Reagan calling on the others for corrective action. But not much is likely to be settled here on either question.

The yen will be the hot economic topic. Since September, when the finance ministers and central bankers of all the summit countries except Canada and Italy agreed to push the nondollar currencies higher, the yen has appreciated about 42 percent against the dollar.

This has brought considerable political pressure on the summit host, Japanese Prime Minister Yasuhiro Nakasone. The yen-dollar relationship will be Topic A at a Nakasone-Reagan bilateral meeting preceding the summit, and in separate sessions of the seven finance ministers, including Treasury Secretary James A. Baker III and Japanese Finance Minister Noboru Takeshita.

The yen-dollar issue aside, the "precooked" summit declaration prepared by the "Sherpas" -- aides to the leaders -- is a bland declaration, the theme of which is that falling interest rates, oil prices and inflation rates offer a benign environment for global advancement.

"It will be the lowest common denominator," said an official who has seen the draft communique. The only other open question is whether the summit will endorse a new multilateral round of trade negotiations meant to broaden the areas of trade covered and to begin "as soon as possible" -- the formulation preferred by France -- or in September, as all the others demand.

Except for the most generalized language calling for cooperative or coordinated policy discussions, the much-advertised question of international monetary reform looms as a nonstarter, with virtually all of the governments unwilling to tamper, for the moment, with the current system of flexible exchange rates.

The sharp rise of the yen is a tender issue here. Nakasone is under fire from the Japanese business establishment, which sees a crunching of its export markets, lower profits and a potential recession.

"We need some kind of stability," said Foreign Ministry official Michihiko Kunihiro.

But the United States and Europe are prepared to argue that the yen must rise more to cut back Japan's extraordinary trade surpluses.

The United States will point to the just-released March figures that show a record $5.5 billion deficit with Japan, despite the costlier yen. Without further depreciation of the dollar, Baker told reporters, the U.S. global trade deficit in 1987 will still be at the "politically unacceptable" level of $100 billion.

In the bilateral sessions, Japanese officials will try to convince their American counterparts that, in effect, the United States may have to choose between a cheaper dollar and higher interest rates. That is, if the dollar continues to decline against the yen, there will be less incentive for Japanese capital to flow into Treasury securities, helping to finance the U.S. budget deficit. To fill that financing gap, American interest rates presumably would have to rise.

There will be some discussion of the widely publicized Maekawa Report, produced by a Nakasone-appointed commission, which calls for a restructuring of Japan's export-oriented society into one driven by domestic expansion. This has developed into a smoldering issue within the ruling Liberal Democratic Party here, some of whose members fear that Nakasone may have promised Reagan action on the report's recommendations that may take years, if ever, to be fulfilled.

The agricultural issue is an old and contentious one between the United States and the highly protective European Community, but this will be the first time that it will be such a specific debating point among the heads of state.

American and European officials appear to be on the verge of a trade war over U.S. charges that Europe, to make it easier for Portugal and Spain to join the community, allowed those two countries to limit imports of American oilseeds and grains. The leaders are expected to refer the farm problem to lesser officials.

The question of faster economic growth in Japan and Europe is another traditional summit issue. It was a key question at the 1978 Bonn summit, when President Carter pressed West Germany's chancellor, Helmut Schmidt, to run a "locomotive" for Western European recovery. The Germans, who claim that their agreement then to boost their economy by an additional 1 percent of gross domestic product resulted in a messy inflation, have balked at calls for another speed-up.

Japan, the United States and most of the Europeans are miffed by the German recalcitrance. They were unhappy that West Germany, the economic leader of Europe, failed to join in reducing interest rates two weeks ago, despite zero inflation and a high unemployment rate of 9 percent. But the Germans make clear that they will not lower interest rates any further. They contend that a prospective growth rate of 3.5 percent or better this year is adequate.

As for Japan, its trade partners are pressing it to drop more import barriers and stimulate its domestic demand to trim back its huge trade surpluses with the rest of the world. But the Japanese are expected to protest at the summit that their domestic expansion is already projected at 4.2 percent this year by international organizations such as the International Monetary Fund. Given the skyrocketing yen, they will ask, how can we be expected to do more?

Glossing over these bread-and-butter issues, all of which translate into job opportunities in each leader's home country, the summit declaration will pay tribute to global economic recovery, the virtues of the private sector and the benefits of "privatization."

The leaders plan to congratulate themselves for a big improvement in the global economic situation since last year, even in the poorer countries still facing a monumental debt overhang. Reagan will claim credit for a more manageable budget deficit situation, with a bow to the Gramm-Rudman-Hollings process. Both Japan and the Western European countries will claim they are making progress in getting rid of "structural" impediments to growth, such as outmoded labor practices in Europe and barriers to foreign investment in Japan.

There will be an endorsement of the so-called Baker "debt initiative," calling for an additional $29 billion in aid to selected Third World debtors in the next three years, and repetition of the need for the IMF and World Bank to achieve better cooperation. But more dramatic responses to the Third World debt problem, such as interest rate concessions, will be ignored.

The leaders plan to cite the sharp drop in oil prices and in interest rates, which have helped to push inflation rates in the seven countries to the lowest levels since 1967.