Billy Carter, who made a comic trademark out of his hard-drinking and fast living, has embarked on a six-week alcohol rehabilitation program which requires total abstinence, lots of hard work and constant "reality therapy" with the staff and patients at the Navy's famed treatment center in Long Beach, Calif.

The patients, who share rooms with three others, are expected to rise at 6 a.m., clean up and maintain their own quarters, and run a mile each day. During the first two weeks, they are not supposed to leave the hospital at all.

"This," said Dr. Joseph Pursch, head of the center, "goes for everyone. They get up. They work. They exercise and they sleep well."

Carter, 41, the president's brother, was admitted to the Naval Alcohol Rehabilitation Service Tuesday evening, after consultation with his personal physician, Dr. Paul Broun, White House physician Dr. William Lukash, and Navy Secretary Graham Claytor, who granted special permission for Billy Carter to enter the facility largely used by military personnel.

"We finally decided we had to do something," said Broun. "He realizes he's been drinking more than he should. He has misused alcohol for some time. The guy has a problem and he's gone for some help."

Broun said the president's brother would pay the $242-per-day fee out of his own pocket.

Billy Carter reportedly drank heavily in the early 1960s, but decreased his intake after joining Alcoholics Anonymous. After Jimmy Carter became a presidential candidate, however, Billy's drinking increased in direct proportion to his visibility, friends say. He also became less controlled in his public utterances, prompting President Carter recently to disassociate himself from what many saw as anti-Semitic remarks made by his brother.

A federal investigation into his operation of the Carter family peanut business, and the attendant publicity, appeared to have been a decisive factor in Billy's decision.

"He's been under a lot of pressure from the press," Broun said yesterday. "He's uptight and anxious."

Broun said he does not believe Billy is an alcoholic. He noted that his patient did without alcohol during his 11-day stay in the Americus, Ga., Hospital recently and he "didn't have any problems."

Pursch said the goal of his "reality therapy" at the Long Beach center is to "get the patient to accept the fact that he has a drinking problem." The "cardinal points" of the treatment are total abstinence, no usage of mind-altering medication, no caffeine, attending AA meetings and group therapy.

"We want them to switch from pills to people and booze to friends," he said.

Both Sen. Herman Talmage (D-Ga.) and former first lady Betty Ford have been treated at the facility, along with countless high-ranking military officers and ordinary soldiers. The overall recovery rate, Pursch said, is 76 percent.