Freddie Prinze, the 22-year-old star of the television series "Chico and the Man," was in critical condition yesterday at UCLA Medical Center in Los Angeles, after firing a bullet through his head at 3:30 a.m.

He left a handwritten, unaddressed note saying, "I can't take it any longer," police said.

Hospital administrator Richard Greene said that the bullet caused severe damage to the brain tissue and "it would be premature for us to offer a prediction as to the chances of survival of disability." Prinze spent two hours in surgery and "tolerated the operative treatment well," Greene said.

Prinze's parents, estranged wife and several friends and business associates reported that they had talked to him during the evening and that he had been depressed and had talked of suicide. His manager, Marvin Synder, was with Prinze in his suite at the Beverly Comstock Hotel when Prinze pulled a gun from a sofa cushion and shot himself.

"Nobody can understand how such a good-looking boy with such a great future could do this kind of thing," said his friend and publicist Paul Wasserman, one of about 25 associates who waited in a converted classroom at the medical center yesterday while surgeons cleaned Prinze's wound.

An actor since the age of 4, Prinze achieved stardom three years ago, portraying a Mexican-American garage mechanic on the hit television show. (This episode scheduled to be shown last night, in which Chico's employer expresses fears that he will become punchdrunk if he attempts to become a prizefighter, was canceled by NBC as "inappropriate for today's events." A show originally scheduled for Feb. 18 was to be substituted.)

Last week, Prinze was one of the stars of the Inaugural Gala at the Kennedy Center, where he delivered a comic monologue about his ethnic background.

His father, a former tool and dye maker, is Hungarian and his mother, who worked in a shoe factory, is Puerto Rican.

Two years ago, Prinze had them quit their jobs and move from the South Bronx into a house he bought them in the San Fernando Valley. They were at the hospital yesterday, Mrs. Prinze insisting that she "won't eat anything until he gets better."

Prinze considered the inaugural appearance "a great personal truimph," said Wasserman, and "he left Washington elated."

But, he said, Prinze was also depressed over his impending divorce and child custody hearings, and had "recently been calling a lot of people - he was depressed, and asking them, 'What does it all mean?'"

Prinze's wife, the former Katherine Cochran, 22, was also at the hospital yesterday. The couple, who met in Jackson Hole, Wyo., in 1975, recently filed for divorce. They had a 10-month-od son, Freddie. The marriage had been the first for him, the third for her.

Prinze's co-star, Jack Albertson, said he was "very closed mouthed about his problems," especially those involving his wife. "He was a good kid, but maybe at 22, the problems were something he couldn't handle," he said.

A friend of Prinze, Jim Markham, said the last time he had seen the comic he was suffering from overwork and complaining about publicity surrounding his arrest, on Nov. 5, for driving under the influence of drugs. Tests at the time had shown evidence of tranquilizers in his blood, and Prinze was scheduled to appear in Los Angeles Superior Court on Feb. 28.

Prinze's television producer, James Komack, and others close to him had visited Prinze Thursday night, in attempts to relieve his depression. Just before shooting himself, he placed a telephone call to his wife.

Komack told reporters that "You've got to remember, this is a 22-year-old kid, with a lot of heavy stuff going on around him. He may seem sophisticated, very mature, but he's still 22, just a New York street kid I picked when he was only 19."

An NBC spokesman said yesterday that six other weekly episodes of "Chico and the Man" have been filmed, but that no decision has been made on how to complete the series' season commitment.