Last April, Dr. Arthur Hull Hayes Jr., commissioner of the Food and Drug Administration, made an official speaking trip to Los Angeles, Seattle and Las Vegas, a visit that cost the federal government $903 in air fare.

While in Seattle Hayes gave a private, after-dinner talk at Virginia Mason Research Center. Four days later he wrote to the center and asked for $832 in air fare for the trip, saying he would "sort things out with Uncle Sam."

Hayes received the $832 from the center, but never repaid the federal government for the air fare.

An examination of Hayes' busy travel schedule last year reveals a picture of a hard-working government official who made a practice of speaking to private organizations for a fee after conducting FDA business, and appeared to allow his official and private expenses to overlap on some occasions. His travel expenses are being examined by the inspector general of the Department of Health and Human Services.

"I haven't done anything wrong," Hayes, 49, said in an interview. "If I have, it has been absolutely inadvertent or because I didn't know some regulation.

"I think I'm a goddamn good commissioner, I think I am an honest person, I know I'm a clergyman and I'm also a good physician. I don't think there is a soul in this world that knows me that thinks I am dishonest or trying to make a buck."

Hayes received $4,300 in honoraria last year for speaking to six private groups on his own time, mostly during trips on which he also conducted official business. These details emerged when Hayes filed his federal financial disclosure statement in January, more than eight months after the legal deadline. He filed the form for the wrong time period, however, and still has not declared his outside income for 1981.

Hayes was paid $500 last May for a private commencement address at Penn State University. After a recent press inquiry, however, Hayes returned the money, saying he had been unaware that his speech was prepared by a consultant who was paid with FDA funds.

Hayes, a well-known cardiologist, said he wrote his other private speeches himself. He said he loses a couple of thousand dollars each year because his official trips cost more than is covered by government travel allowances. His annual government pay is $79,662.

"I appreciate that some people in government are supposed to be cleaner than Caesar's wife and all the rest of it, but one also still has to live," he said. "Quite honestly, my time in government is a hiatus. It would be quite different if I were planning a whole career and had to organize myself thereby. This is not anything different than I have done all my professional career. And I must confess I don't see anything wrong."

Hayes made more than 40 official speeches last year. Fifteen of these were out-of-town trips, including visits to London, Cairo, Nassau, San Juan and Aspen, Colo.

One such official trip began last April 25, when Hayes flew to Los Angeles to address the National Association of Chain Drug Stores. The next day he flew to Seattle to visit the FDA regional office.

That evening Hayes delivered informal after-dinner remarks to the trustees at Virginia Mason Research Center. The center provided him with a $1,500 honorarium and paid his $82.50 bill at the Park Hilton Hotel.

After a day's personal leave Hayes went to Las Vegas to address the American Pharmaceutical Assocation. Upon returning to Washington he wrote Virginia Mason and said he would accept its original invitation to pay his first-class air fare to Seattle.

"Since part of this trip was for other reasons," Hayes wrote, "I think perhaps it would be fair, and keep my accounts with the government straight, if you reimburse me personally for the round trip, first-class air fare from Washington, D.C., to Seattle, which is $832. I then will sort things out with Uncle Sam."

In interviews, Hayes first denied that Virginia Mason paid for his trip, then said the money was meant to upgrade his government coach tickets to first-class fare. He said the government still had to be billed for the trip because it is against FDA regulations for a private group to pay travel expenses for an official commission trip. Switching to first class would have cost no more than $500, or less than the $832 Hayes received.

Hayes said he doesn't see any problem. "What expense would I have repaid the government for?" he asked. "It's got nothing to do with the government . . . . The government didn't get cheated at all."

Hayes said he has not allowed private firms or trade groups to pay travel expenses for his official speeches. After returning from the West Coast for a White House meeting, however, Hayes was able to speak at a science center in Philadelphia that night, when Hershey Foods sent a private plane to fly him to and from Washington.

FDA regulations allow officials to accept honoraria and expenses to address groups that are not regulated by the FDA, as long as the speeches are delivered in a personal capacity and do not create a conflict of interest. Hayes said none of the groups he addressed privately is regulated by the FDA.