In the tar-like shadows of the rehearsal room, the band plays "New York, New York" and a breathy, deep voice skips the words and bleeps "blah, blah, blah."

This is Diahann Carroll on a Saturday afternoon, warming her throat, testing lights, signing for the few autograph seekers who have braved the locked doors. This is anything but the blahs. This is Diahann Carroll, kissed by her success on "Dynasty," taking on the latest breathtaking spin of a successful but sometimes forlorn roller coaster of a career.

"Television has an incredible impact, that is the immediacy of the recognition. I have been fortunate enough in the last season and two episodes before to have attracted an audience that is quite young. 'Dynasty' does cross the board in terms of the age of the audience. So the young people who are too young to remember 'Julia,' and had no knowledge -- they might have heard the name but weren't really clear as to what it was, it has become a clear image for them," she says.

As the hour-long rehearsal breaks up, Carroll takes a few minutes to discuss the character Dominique Deveraux, the driven woman she emphatically calls "the first black bitch on prime-time television," and how the current crest of fame fits into a re'sume' that goes back to a part in the musical "House of Flowers" in 1955.

Still recovering from the red-eye flight from Los Angeles, Carroll wears dark glasses, but her wide-set eyes look directly at each person she talks to. And her beauty lives up to all the advance notices: a soft, oval face with a square mantle of a chin, a smile that lights up girlishly but can fade into the sneer she needs for all the Carrington madness. She has asked that the air conditioning be turned off but she never removes a fur aviator-style jacket.

"I mean that," she says of her "bitch" description. "Very often it has been made light of. I think it is important that we allow actors who represent the Third World to portray roles that are not necessarily sympathetic. And the other end of the spectrum that we are offered very often is we are so sympathetic, so wonderful, so good and so marvelous that we are totally unbelievable. Somewhere in the middle, I thought it would be interesting to try to create a new character. There are some things about Dominique that are perfectly likable, there are other things that are completely self-centered. And I think she will remain that way."

The character of Dominique, as part of the lavish soap that is ABC's most popular program, is not only making its own mini-mark but accelerating what had been a lagging career. Carroll made the cover of TV Guide last week. On Wednesday, she wrapped up another episode of "Dynasty," and she has been signed for next season. On Friday, she was interviewed by Barbara Walters for a special to be aired May 28. Saturday morning, she arrived in Washington to appear that night at the annual dinner-dance of the Women's Committee of the Washington Performing Arts Society. Then she was back on the plane early yesterday for a party in Los Angeles for "Love Boat" and its guest stars; she was the 100th.

Carroll, 49, who grew up in New York City as Carol Diahann Johnson and graduated from the New York High School of Music and Art -- the "Fame" factory -- began modeling when she was 15. Soon she was appearing on the Jack Paar show and in black movies such as "Carmen Jones," and then costarred in "No Strings," a hit musical about an interracial romance. In 1968, she starred in "Julia," the first black woman in a prime-time series. Her portrait of a financially comfortable, nonpolitical nurse in the late 1960s was successful but at the same time denounced as too distant from the reality of black life. Afterwards, she seemed to make up for that criticism with her makeup-less portrait of a welfare mother in "Claudine," which earned her an Academy Award nomination in 1974, and with a much-praised performance as Elizabeth Ashley's replacement in the play "Agnes of God."

For now Carroll is relaxed with the latest burst of praises, is dating singer Vic Damone, whom she describes as a "good friend," and the question of a black woman playing almost raceless roles does not hound her. Recently she received a Career Achievement Award from Ebony magazine, which she accepted by saying, "You and I, we've fallen out a few times," referring to the criticism she had sometimes received from black audiences.

"Through time, which is the great healer, we have all come to a greater understanding that 'Julia' was pertinent, very important and possibly made one of the most important inroads in terms of presenting Third World people on television in family situations," she says. "And that is what we wanted to do. We are more sophisticated now, we don't require of our Third World artists total explanation as to why they have accepted this role, why not a different kind of presenting the role."