Vicki Morgan, who last year brought an $11 million palimony suit against the late Alfred Bloomingdale, a friend of President and Mrs. Reagan, was beaten to death with a baseball bat early yesterday in Los Angeles.

At 3:20 a.m., Morgan's roommate, Marvin Pancoast, walked into a North Hollywood police station and said to an officer, "I just killed someone." The 33-year-old Pancoast told investigators that he and 30-year-old Morgan had been arguing over finances and that he waited until she had gone to sleep to hit her. Police found Morgan's body sprawled across a bed, with the bloody bat nearby. Pancoast has been booked for investigation of murder.

Morgan, a former model and actress who has not worked since filing her suit a year ago today, met Pancoast in 1979. He had been employed for 18 months as a Xerox operator at the William Morris Agency, a job he left in January. The couple had been living together for only three weeks and had planned to move into separate apartments yesterday. Police said the three-bedroom condominium they shared was filled with packing boxes.

Pancoast, a tall, thin, blond-haired man, "seemed to be a pleasant person, but we knew nothing about his personal life," said William Morris vice president Roger Davis. According to Morgan's former lawyer, Marvin Mitchelson, she had been meeting recently with agents at William Morris to discuss the sale of book and movie rights to her life, although Davis emphatically said, "I don't know anything about that."

Mitchelson said, "She took a lot of secrets to the grave with her." Morgan claimed to have worked for a brief time on the Reagan campaign in Los Angeles, and swore in a deposition that Bloomingdale often shared "secret and delicate" details of White House meetings with her.

In her $11 million suit, which she continued to press after Bloomingdale died last Aug. 23, Morgan claimed that for 12 years she had served as a therapist to help the founder of the Diner's Club and the heir to the Bloomingdale's department store chain "overcome his 'Marquis de Sade' complex." Morgan said that Bloomingdale had a "Jekyll and Hyde" personality, and testified that she often watched as other women stripped, let Bloomingdale bind them with neckties and then crawled on the floor as he rode on their backs and beat them, while he drooled. The trial became so sensational that White House aide Morgan Mason met with Mitchelson to suggest some compassion for Bloomingdale's wife, Betsy, a close friend of Nancy Reagan.

Morgan's suit was filed after Betsy Bloomingdale discovered her husband's affair with Morgan and then stopped his $18,000 monthly payments to the other woman while he was in the hospital.

Last fall Los Angeles Superior Court Judge Christian Markey dismissed most of Morgan's suit, claiming that her relationship with Bloomingdale was "no more than that of a wealthy, older, married paramour and young, well-paid mistress . . . and was . . . explicitly founded on paid sexual services."

Morgan also sought $1 million under contracts Bloomingdale signed in February 1982, while hospitalized for cancer, in which he promised her half his interest in Show-Biz Pizza franchises. A trial on that issue was pending, and attorneys for both Morgan and the Bloomingdale estate said it is unclear what impact her death will have on the litigation. Morgan is survived by a 14-year-old son, Todd, who was visiting his grandmother at the time of the death.