Since he left the White House in January 1977, Gerald Ford has become something of an itinerant professor. Yesterday, the former president said at American University, he has visited 39 colleges in the last 23 months, taught about 270 classes, and answered about 4,000 questions from inquiring students.

"I find that the questions are more stimulating, at least to me, than my remarks," Ford said as 300 students in the American University chapel laughed appreciatively. Ford smiled and laughed too.

The questions that followed ranged from Iran to inflation, from U.S. military strength to Ford's plans.

His shortest answer, which was the only one to draw sharp applause, followed a question about former president Nixon's recent statement that he plans to speak out about politics again.

"I would hope he would stay in the background," Ford said. "Next question."

Beside the brief speech and questions in the university chapel, Ford also spent 45 minutes talking briefly and then answering questions from about 70 law students.

Even though security was tight with a phalanx of Secret Service agents and a dog sniffing lockers for bombs, the atmosphere of both sessions was lively and informaal. The response Ford received was warm.

"It was so informal, it was nice," said Mark Au, 19, a sophomore from Hawaii. "I didn't expect that. Maybe someone should have put him on the spot more. But he sure knows his business very well."

For his talk to the lawstudents Ford stood at the front of a small moot courtroom - below a raised jedge's bench, not on it. He spoke without notes.

The theme of the speech was that Congress had encroached too sharply on the power of presidents in both domestic legislation and foreign policy.

"The pendulum has swung so far," Ford said, "that you could almost say we have moved from an imperial presidency to an imperiled presidency. Now we have a Congress that is broadening its powers too greatly."

Although most of his comments were nonpartisan, Ford strongly attacked the Carter administration about inflation, which he said now is double the rate it was when he left office.

"If you've ever driven in Michigan on an icy road going down a hill," Ford said, "the current situation reminds me of that . . . Now they've slammed on brakes, but they should have done it earlier. Nobody knows where (the economy) is goung-into this ditch or that ditch or over the precipice."

Would Ford run for president again in 1980?

"Well, I've been so preoccupied with other things." the 65-year-old former president said, ". . . that I honestly haven't focused on my own future . . . All I can say is that I am very healthy and I won't duck any responsibility."

As in most of his visits to college campuses, Ford's talks yesterday were sponsored by the American Enterprise Institute, a Washington-based "think-tank" that pays him $50,000 a year to be a "distinguished fellow."

The colleges visited have been in all parts of the country, including private universities such as Yale, large state universities such as Kansas and Michigan, and black colleges such as Tuskegee.

Audiences have ranged from 12 students in an economics seminar at the University of Alabama last spring to 18,000 at a studeent forum at Brigham Young University last week, a Ford aide said.

American University is the first college Ford has visited in the Washington area.

James Shuman, a former White House press officer who now helps Ford arrange his academic trips said the visit to American University went "the way it usually does . . . Initially there is a great curosity that a former president is going to come. But the barriers break down and there's a nice give and take."

At American, tickets for Ford's appearances were given out last week on a first-come, first-served basis. Officials said the tickets were snapped up in less than an hour. One student said he paid $20 to a ticket-holder to get inside. Another said he was offered $50 for his ticket, but turned it down. CAPTION: Picture, Former president Ford addressing the American Enterprise Institute: The courts and Congress are making the "imperial presidency . . . an imperiled presidency." By James K. W. Atherton. The Washington Post