Ronald Reagan has mellowed after four years in office, lowered the level of his anti-Soviet rhetoric and raised his understanding of international affairs, according to government officials and political observers questioned last week in six world capitals.

The postelection consensus that emerged in interviews by The Washington Post was that President Reagan -- like other second-term American presidents -- is moving into his final term with a heightened awareness of how history will judge him as a peacemaker.

The one clear exception to this upbeat view was found in Nicaragua. There, after a weeklong post-election furor over U.S. suggestions that the Soviet Union may have delivered warplanes to Managua's leftist government, Reagan was perceived as having gone out of his way to be belligerent. Europeans also expressed anxiety about Reagan's intentions in Central America.

By and large, however, the president is moving into his second term as the beneficiary of a clear evolution in how he is perceived internationally. No longer is he seen as a foreign policy neophyte more intent on a U.S. military buildup than on controlling East-West tensions.

The fear of a U.S.-Soviet nuclear confrontation that spread across Western Europe during the president's first term, sending hundreds of thousands into the streets to protest the deployment of new nuclear weapons, has subsided.

"Reagan's real foreign policies have become much more prudent, much more traditional," said Dominique Moisi, associate director of the French Institute for International Relations in Paris.

Echoing views held in several world capitals, Moisi added: "What people feared here is that Reagan's real policies might come to resemble his declared policies. But this did not happen in the first term and it is unlikely to happen in the second."

The president's inability, despite his landslide victory over Walter F. Mondale, to gain a strong Republican advantage in Congress was also seen as a moderating and positive outcome of the last week's election. Just how moderate the president's second term is likely to be depends, in the view of many, on who will emerge in the White House and the Pentagon as key influences on the president's foreign policy.

In the Soviet Union, particularly, Reagan watchers were waiting to assess the outcome of what they see as a power struggle within the administration.

"Foreign and military policies are one of the critical arenas where various factions within the administration can be expected to fight it out," said Sergei Plekhanov, a department head at the U.S.A. and Canada Institute. Soviet observers indicated they would be watching closely as the administration put together its team for a second term, paying attention to the role assigned to hard-liners.

"If key [moderate] people stay -- people who are known, whose opinions are known, it is difficult to expect that something will happen," said one Soviet specialist.

Thus far, the Reagan administration has indicated there will be no major changes among senior White House officials, with the possible exception of deputy chief of staff Michael K. Deaver, who may leave early next year after directing planning for Reagan's second inauguration.

While several senior Soviet officials recently have warmed to the possibility of arms talks with the United States, there was puzzlement last week in Moscow over a senior Reagan administration official's announcement that the Soviet Union had asked specifically about arrangements for "umbrella" talks with Washington on arms control issues. Those talks, the official said, would be between Secretary of State George P. Shultz and Foreign Minister Andrei A. Gromyko.

Sources in Moscow said they had no idea what the Reagan administration official was talking about and suggested that the announcement, made Thursday in Santa Barbara, must have been aimed at influencing American public opinion.

In the Middle East, Reagan's reelection was viewed positively -- but with radically different expectations -- by Israel and several Arab nations.

In Jerusalem, Reagan is seen as a known quantity, a proven supporter of Israel who is unlikely to change his way of thinking or his underlying philosophy. Because of this, the often stated belief that a second-term president is likely to put pressure on Israel appears to be discounted.

Moreover, the Israelis interviewed foresee Reagan as unlikely to embark on major new initiatives in the Middle East peace process, because of the intractable nature of the issues and because the administration will be preoccupied with other foreign policy questions.

"There is already a crisis in Nicaragua, the Lebanon situation is not over, there is the nuclear-arms issue," an official said. "An administration is not built to deal with more than one or two crises at a time."

A specialist on U.S.-Israeli relations with close ties to the government of Prime Minister Shimon Peres said he expected Reagan's Sept. 1, 1982, initiative to "remain on the table as the American proposed agenda" for the peace process. But he said that activating the proposal -- which called for a Palestinian "entity" in "association with" Jordan in the Israeli-occupied West Bank -- would depend on the Arab states of the region.

In Egypt and Saudi Arabia, senior officials said they expect more independence of Israel and willingness to press it into accepting a regional peace plan.

Reagan's reelection, for many Arab allies of Washington, has raised hopes of an international conference on the Middle East in Geneva, if only to discuss possible approaches to a settlement of the Palestinian question and set up smaller negotiations among countries directly concerned.

Finally, although Reagan's reelection was not accompanied by a conservative realignment in Congress, political observers around the world were nevertheless impressed by the president's personal popularity among American voters.

For the Soviets, especially, Reagan's political appeal was viewed as a powerful reality that could not be underestimated. One Soviet analyst said much depends on Reagan's "personal ambitions" to be seen by history as a peacemaker, and whether his advisers will permit him to realize such ambitions.