In a rare, on-the-record appearance before journalists, cartoonist Garry Trudeau today said he's "enjoying being back" with his "Doonesbury" comic strip and defended his insistence that newspapers carrying the strip print it in larger-than-standard size.

Trudeau also replied to critics he said have sent him hundreds of letters "expressing doubts about my sense of humor and patriotism" in response to his biting satirical portraits of President Reagan and Vice President Bush during the presidential campaign.

"Satirists are not supposed to be balanced," he told editors at an Associated Press Managing Editors convention here. "They are supposed to be unfair." And he added, "Humor is what allows Art Buchwald to have lunch with those he writes about. Satire is deadly serious."

Portraying himself as a champion of cartoonists, Trudeau said that his colleagues have been helpless in attempts to prevent editors from steadily shrinking comic strips. He accused editors of taking comics for granted, like "public utilities," and said that even syndicates have "successfully intimidated their artists" by telling them that if they didn't accept smaller formats, they would appear in fewer newspapers.

Trudeau said he did not intend to be "arrogant" by demanding that editors who bought "Doonesbury" after his 20-month hiatus publish it roughly 25 percent larger than most other strips that now appear in newspapers. "Many editors," he said, "turned a reasonable, modest format stipulation into a personal challenge" of their control over the content of their newspapers. He said that he hoped other cartoonists would follow his lead, but acknowledged that editors so far have treated "Doonesbury" as an exception, and in many cases displayed it away from other comics, as The Washington Post does. "I find it more than a little embarrassing," Trudeau said. "I think it is time for you editors to listen to your partners, and that's us, the artists and the syndicates. We've always had to be the ones to compromise."

He added, "Doonesbury happens to be the only strip whose size I have control over."

Trudeau also reacted strongly to what he said was widespread criticism of his decision to stop drawing "Doonesbury" to pursue other interests. "The public noise over my leave of absence and return was totally out of proportion to the event," he said; and the leave was "perfect" for the task of repositioning his characters in time. "I thought it was important for my characters to remain representative of my sensibility" and of others of his generation in the resumed strip. "I left at a time when I felt reader interest could be sustained," he said.

Trudeau, who last appeared before APME in 1972, declined to state his opinions on national affairs or to "pontificate on trends in this country." Said Trudeau, "I feel my strip is my best avenue of expression."

He did, though, attribute both President Reagan's landslide reelection victory and widespread criticism of his strip to a wish by Americans to feel better about themselves. It reminded him, Trudeau said, of a woman who once told a TV sportscaster following Secretariat's Triple Crown racing victory, "After the traumas of Vietnam and Watergate, Secretariat restored my faith in humanity."

"Ronald Reagan," Trudeau said, "is the Secretariat of the '80s."