Roger L. Stevens, the chairman of the Kennedy Center board of trustees, suffered a moderate heart attack early Saturday morning in San Francisco, according to his physician there.

Stevens, 69, is in stable condition, according to Dr. Francis L. Chamberlain, a cardiologist at the Franklin Hospital of the Ralph K. Davies Medical Center in San Francisco, who is attending Stevens. "He's talking, reading the paper, smiling," said Chamberlain yesterday afternoon in a phone interview, and the prognosis "looks very encouraging. He's gotten through the most difficult period -- the first three days."

Dr. Chamberlain added that "normally these patients can resume their activities."

Champerlain described the problem as "a definite coronary of moderate degree" and said "he will be here in the hospital for a good three weeks." Stevens' wife, Christine, flew to San Francisco this weekend to be with her husband. Stevens is in a cardiac-care unit where his heartbeat can be constantly monitored.

Stevens had flown to San Francisco Friday morning for an all-day meeting of Folger Library trustees followed by a dinner. He had returned to the Bohemian Club, where he was staying, went to bed, and awoke late in the night with chest pains.

He called his doctor, who ordered him admitted to the Franklin Hospital at 3 o'clock Saturday morning.

Previously, Stevens had flown from Washington to Los Angeles to arrange "contacts in connection with the upcoming Kennedy Center Gala," according to the Center's director of operations, Thomas Kendrick. The annual event, planned for early December, honors five noted American performers in the arts. Stevens was to have flown on to New York yesterday morning for a few days.

Kendrick said that Kennedy Center operations would proceed as usual despite Stevens' hospitalization. "There's a professional staff that runs the Center," Kendrick said. "Stevens has been away for three- and four-week periods before."

In 1970, a year before the Kennedy Center opened, Roger Stevens suffered a heart attack after which he returned to work.

The planned Kennedy Center board of trustees' meeting also is expected to be held as planned on Oct. 18, Kendrick said. "There are two vice chairmen -- Sen. Charles Percy (R-Ill.) and Henry Strong [of the Hattie Strong Foundation] -- and one of them will chair the meeting," said Kendrick.

Kendrick said he has been awed by the rapid-fire pace of Stevens' nonstop schedule. "He's got 12 meetings a day, and he's in the air half the time. He's gone from morning to night. His schedule is like three people's schedules combined."