ACTORS Equity has rejected a bid to bring the entire British cast of the acclaimed Royal National Theater’s revival of “Oklahoma!” to Broadway in the fall.

The decision threatens to scuttle the New York production and sets the stage for a possible showdown pitting the union against the revival’s director, Trevor Nunn, and its producer, Cameron Mackintosh, who has battled Equity in the past.

Nunn and Mackintosh asked the union to approve the British company because of Nunn’s demanding schedule, which would make it impossible for him to cast and rehearse American actors for the Broadway production of “Oklahoma!”

“We have not sought to have any confrontation with Equity over this,” Mackintosh said by phone from London yesterday. “It is simply a practical matter. Trevor would love to be able to put in an American cast, but he just does not have time to do it” in the fall.

The ruling on “Oklahoma!” was made this week by Equity’s alien committee, which oversees requests to bring foreign actors to the United States. The decision can be overturned by the Equity council, the union’s highest governing body. Nunn will argue his case before the council in New York next month.

If Equity affirms the initial ruling, Mackintosh said the revival may not get to Broadway for at least two or three years – if ever.

“What is at stake is the momentum of the show,” he said.

“Oklahoma!” opened to rave reviews last summer at the National. It won the Evening Standard Award for best musical and was nominated last week for nine Olivier Awards, London’s version of the Tony Award. Mackintosh, the producer of “Les Miserables” and “Miss Saigon,” moved the revival to a commercial theater in the West End and would be the producer on Broadway.

Nunn, who is also the artistic director of the National Theater, could not be reached for comment. But he spelled out his predicament in a letter to Mackintosh, a copy of which was obtained by The Post.

His “punishing schedule,” he wrote, “means that I couldn’t be starting work on the show again from scratch. … So the only way my production of ‘Oklahoma!’ can get to New York is if the original [British] company play the opening few months. That way, I would have time to explain to an American production team how the show was arrived at. I could attend final auditions for an American cast to take over, and do final rehearsals with them at a later stage.

“My request,” he continued, “proceeds from necessity and not at all from any xenophobic or nationalistic response. I would love to do a full rehearsal period with an American cast, but I can’t.”

(The British production features two American actors and was choreographed by Susan Stroman, who is also an American.)

If the show gets to New York – and is a hit – Mackintosh said it could spin off one or two national companies, providing work for many American actors in the future.

Actors Equity’s executive secretary, Alan Eisenberg, did not return calls seeking comment. But Equity sources say the union is divided over the issue.

Some members agree that a successful “Oklahoma!” – even if initially cast with British actors – eventually would provide work for American actors on Broadway and on tour.

But others argue that Equity cannot allow English actors to be cast in a Broadway production of the quintessential American musical, by Richard Rodgers and Oscar Hammerstein II.

Those who are opposed to a British “Oklahoma!” are also salivating at the chance to settle old scores with Mackintosh.

The powerful producer bested Equity in a 1990 battle over the casting of Jonathan Pryce in the Broadway production of “Miss Saigon.” He beat the union again in 1996 when he dismissed several actors from “Les Miz” on Broadway.

But Mackintosh doesn’t see the need for yet another titanic struggle.

“We are not trying to be combative,” he said. “We just want to bring this terrific production to New York. And this is the only way we can do it.”