Doctors have found a new tumor in Republican National Committee Chairman Lee Atwater's brain, and his mother flew to Washington yesterday to be at his side, close friends said.

Atwater, the political strategist who orchestrated George Bush's 1988 presidential campaign, was admitted to George Washington University Medical Center on Aug. 2 after experiencing a high fever and severe back pain.

Diagnostic tests disclosed what doctors termed "tumor progression." A biopsy on Monday showed the tumor to be malignant, and Atwater underwent more radiation treatments Wednesday.

Friends and associates who have until now been upbeat about Atwater's condition said Friday his condition seems to be deteriorating. The friends, who spoke on the condition that they not be identified, said Atwater is alert, able to speak and joking even though he is heavily medicated with morphine.

Medical experts not connected with Atwater's case said the prognosis is poor.

Edward Oldfield, chief of neurosurgery at the National Institutes of Health, said multiple, separate tumors in the brain are extremely rare. He suggested that the new growth in Atwater's brain may be an offshoot of the original tumor, which was the size of a dime.

The first cancerous tumor was discovered in March after the Atwater, 39, collapsed while addressing a Republican fund-raiser.

On April 3, Atwater received radical radiation treatment to destroy what his attending physician called a rapidly growing tumor.

Officially, the RNC was trying to put the best face on what some staffers acknowledged was a sad turn of events.

"Nothing has changed. Lee is getting radiation. He is still alert and joking," said RNC press secretary Leslie Goodman.