As he was two years ago, Frank Sinatra will be the featured entertainer this fall when Mrs. Marvin Davis, wife of the oil tycoon who just bought 20th Century-Fox studios in Hollywood, stages her "Carousel Ball" for the Children's Diabetes Foundation at Denver.

That may not sound like such a hot piece of gossip in itself. But the increasingly close friendship between the controversial superstar and the Davises is something to watch.

Does it mean that Sinatra will once again occupy Shirley Temple's old dressing rom on the Fox lot?

It was a big status symbol in years gone by when Sinatra moved his secretaries and entourage into the building -- during the making of the movie "Von Ryan's Express" in 1965 -- and continued to use the facility long afterward.

"A lot of people on the lot wanted to know why," one Fox executive said last week.

Sinatra lost the use of the cottage a decade ago when tough-minded Dennis C. Stanfill, who resigned last week after a bitter power struggle, arrived on the scene at 20th.

Stanfill, who came to the studio as executive vice president in 1969 and was its head for more than a decade, had at first seemed to have Davis' confidence when the maverick oilman took control last spring. But Stanfill departed saying his contract had been "materially breached."

Meanwhile, Sinatra and Davis and their wives, both named Barbara, are very close.

The Sinatras and the Davises both have houses at Rancho Mirage.

"They're our neighbors in Palm Beach and they've been friends of ours for years," Mrs. Davis said last week. "He's been just wonderful."

The Davises were among those present when Sinatra gave a small, sit-down dinner for 24 at his Palm Springs compound to celebrate the 25th anniversary of Princess Grace and Prince Rainier during their U.S. visit in April. The royal couple's three children and the Davises' oldest daughter, Patty, also attended.

The Carousel Ball, which the Davises give every year, will raise $1.3 million this year, according to Barbara Davis. Last year the ball raised $1 million.

Sinatra "has been very, very nice in helping the cause of juvenile diabetes," she said. "All of these people donate their talent.

"When he comes, his friends come. Cary Grant and Dinah Shore are coming this year.

"Last year Sammy Davis Jr., Bob Hope, Telly Savalas and Danny Thomas came."