Leslie Uggams has some nerve. That's "some," as in lots of. Just 24 hours after Diahann Carroll was forced to bow out of "On Golden Pond" with a back problem, Uggams agreed to step into Carroll's role opposite James Earl Jones in the highly anticipated revival at the Kennedy Center.

And that's not the half of it. Uggams, who went into rehearsal yesterday, has less than one week to get Ethel Thayer, the big-hearted wife and mother of Ernest Thompson's family drama, into her bloodstream. Performances are scheduled to start Tuesday, and the show's producer insists there will be no delays.

Injured stars are nothing new, and often, when a performer of Carroll's renown withdraws this close to an opening, the production is postponed or even canceled. For example, after Tommy Tune broke his foot in 1995 during the tour of the Broadway-bound musical "Busker Alley," the show was never heard from again. At other times, injuries have been incorporated into a portrayal, as was the case with the late Danny Kaye, who played his leading role in the musical "Two by Two" in a wheelchair after tearing a ligament.

There have even been times when chorus members and understudies have vaulted to fame after a star's mishap or illness -- witness Shirley MacLaine's abrupt ascension in "The Pajama Game." The "On Golden Pond" incident seems just as exceptional: A well-known actress is willing to cook up something like a polished star turn in the time it takes to drive cross-country.

"It was devastating not to continue with Diahann," said Jeffrey Finn, the play's producer. "Unfortunately, Diahann has a herniated disk that became worse during the rehearsals to the point where she wasn't able to walk. Then it got to the point where her doctors were saying, 'Diahann, the most important thing is your health.' "

Carroll, 69, was rehearsing with Jones and other cast members in New York. Over the weekend, according to two people associated with the production, she began to experience great pain, and by Monday she became convinced that she would have to return to her home in Los Angeles to recuperate. Finn said that upon learning of Carroll's decision, he consulted Jones and the play's director, Leonard Foglia, and started an immediate search for an actress to take over the role.

No thought was given to canceling the production, which is to run from Tuesday until Oct. 17 in the Eisenhower Theater. The feeling, according to some involved in the show, was that Jones provided star power enough, and as a final backup, the production could have elevated Carroll's understudy, Petronia Paley.

Ticket sales have been robust, with more than 60 percent sold already, said Tiki Davies, director of the Kennedy Center's press office.

A postponement was not an option either, because the Eisenhower is tightly booked; the Washington Ballet performs there three days after "On Golden Pond" closes.

The prospects for the production after Washington -- it is also scheduled to play Wilmington, Del., and Finn says his eventual plan is Broadway -- are no doubt enhanced with a second "name." Several well-known actresses were talked about before Finn made a personal appeal to Uggams, who agreed Tuesday and was in the rehearsal room the next day.

Uggams, 61, won a Tony Award in 1968 for her performance in "Hallelujah, Baby!," a musical that is being revived this season at Arena Stage. Though she's sung in Las Vegas and Atlantic City, Uggams has been seen ever more frequently of late in stage dramas, from regional presentations of "Master Class" to the Broadway production of "King Hedley IV," for which she received a Tony nomination.

The play in which she will now appear, about recrimination and reconciliation in the lives of a retired couple and their resentful daughter, had a modest run on Broadway in 1978 and 1979, but found much broader success as a 1981 movie with Katharine Hepburn, Henry Fonda and Jane Fonda. Hepburn and the elder Fonda won Oscars for their portrayals.

Some relieved hands in the new "Pond" think Uggams deserves an award just for showing up.

"She's digging in with the enthusiasm you'd expect of her," Finn said yesterday. "We're all rallying around her."

Diahann Carroll and James Earl Jones rehearsing "On Golden Pond" in New York last week. Carroll has dropped out of the project for health reasons.