As he winds up a leisurely second week of cross-country campaining, Ronald Reagan is finding it increasingly difficult to restrain himself on the subject of American retaliation against Iran.

In speeches, receptions and conversations with reporters, the former California governor is talking more and more forcefully about the Iranian issue and calling upon the United States to grant political asylum to the deposed shah, if he wants it.

Usually, the heaviest applause comes when Reagan says that Carter administration policies of "weakness and vacillation" led to the situation that made the taking of hostages possible. Another applause line is Reagan's declaration that he would make the United States respected once again "so that no dictator would dare invade a U.S. embassy and hold our people hostage."

Reagan gives the impression of being a restrained but impatient warrior, anxious to bring U.S. power to bear against what he calls "a demented dictator" and the "rabble" who hold Americans hostage in their own embassy.

Recognizing that President Carter is involved in a highly sensitive negotiation process aimed at security freedom of the hostages, Reagan has tried to walk a thin line between pronouncements that could endanger the lives of the hostages and his deeply felt criticism of Carter's foreign policies.

However, in an interview Thursday, Reagan suggested for the first time that he might make the Iranian issue a major theme of his political campaign once the hostage question is decided.

As long as there is hope for getting the hostages back alive, Reagan said, political candidates should restrain themselves in the interests of national unity.

But he added, "If there comes a time when the decision has been lost and their fate has been determined by the [Ayatollah Ruhollah] Khomeini, then that's a different matter. Then I think, though it sounds like Monday morning quarterbacking, we should hold the man [Carter] to what was done and what options were there -- what were the things that weren't done that might have been done . . . ."

One of those things, Reagan contends everywhere, is that the United States should have done more to keep "a great ally," the shah, in power.

Considering that he is the acknowledged frontrunner for the Republican presidential nomination, Reagan has been campaigning in relative obscurity during this second swing of his candidacy.

Partly this is because of the long shadow cast by Iran over every candidate's campaign. Partly, it is because Reagan has been lightly covered by the press during the course of a week that has taken him to Arkansas, Alabama, Illinois, Iowa, Minnesota, Washington state and, today, to Alaska, fulfilling longstanding obligations to address Republican fundraisers.

Only nine news organizations were regularly represented this week aboard the Reagan campaign plane, which has unofficially been dubbed the Ponce de Leon, after the seeker of the mythical fountain of youth. Forty-six news organizations were represented on the first Reagan campaign tour two weeks ago.

Reagan has received some good political news as he travels around the country -- first from his organizers in Iowa, where he was told that he is leading George Bush, and then in Minnesota, where Rep. William Frenchzel (R-Minn.), the Bush chairman in the state, told a reporter that Reagan had a healthy lead among Minnesota Republicans.

Reagan was well received by Minnesota Republicans at a Mankato fundraiser that celebrated the 36th birthday of Rep. Tom Hagedorn (R-Minn.), the only Minnesota congressman who has so far endorsed Reagan. But Reagan blunted his performance by mistakenly calling Hagedorn "Bob" after Hagedorn had introduced him to the gathering.

Interviews of eight persons at a reception preceeding this fund-raiser turned up only two who were unreservedly committed to the Reagan candidacy. The others said they wanted to wait before making any commitment, as did four of five persons interviewed at a Chicago fundraising reception. The responses appear to reflect the earliness of the campaign more than anything else, but some Republicans mentioned the subject of Reagan's age, 68.

"I don't believe he's any more infirm than I am." said a healthy-looking 55-year-old Chicago businessman who supported Reagan in 1976. "I'm for him now and I expect to be for him in 1980, but I want to see how he holds up."