Santa's had a sex change. Or at least the Santa who popped in at PR impresario Roy Pfautch's annual Christmas fete benefiting Toys for Tots last night at the J.W. Marriott. The voice was a little bit higher, and the padding was in all the wrong places, but Santa's knee was strong enough to bounce the likes of Barbara Bush's press secretary, Anna Perez; Canadian Ambassador Derek Burney; Sally Atwater; White House Communications Director David Demarest; Marine commandant Gen. Alfred M. Gray Jr.; and presidential spokesman Marlin Fitzwater. Each year, Pfautch has a mystery Santa pass out warm greetings and goofy gifts (this Santa gave Fitzwater a bottle of hair tonic "because you have the hairiest job in town." Ho ho ho), and after all the fun, the audience gets a peek at who's hiding behind that fuzzy white beard. But not this year. Protesting that she "looked awful," Santa sprinted out of the ballroom, up the escalator and into a Dodge van that was waiting to whisk her home to the vice president's mansion, laughing all the way. A Holiday Message

The Saudi ambassador to the United States, Prince Bandar bin Sultan, in a gesture of seasonal goodwill, has mailed Christmas cards toinfluential Washingtonians. The message inside the card is a passage from the Koran: "Behold, the angels said: 'O Mary, God giveth thee tidings of a Word from Him: his name will be Christ Jesus, the son of Mary, held in honour in this world and the Hereafter and of {the company of} those nearest to God.' " Jesus is considered one of the prophets in the Islamic religion.

But the name of the man whose birthday the Christian world will be celebrating on the 25th is not being mentioned on the radio broadcasts to the U.S. troops in Saudi Arabia. Melvin Russell of the Armed Forces Radio and Television Service in charge of programming said yesterday that no music with religious lyrics is being carried to the troops. "It's their country and we are sensitive to their beliefs," Russell said. "If there are lyrics in the music and they are of a religious nature, we will not air it," adding that instrumental music will be big this season.

Greetings From the White House George and Barbara Bush are mailing out their Christmas card this week to 145,000 people. The message reads: "The President and Mrs. Bush extend their warmest wishes for a merry Christmas and a new year that will bring harmony to our world and happiness to you and those you love." The watercolor of the Oval Office with a decorated Christmas tree beside the president's desk was done by Mark Hampton, an interior designer and artist who has worked on the restoration of the White House and Blair House. The White House said the Republican National Committee was paying for the printing and mailing costs.

Czech Ambassador Back at Home Czechoslovakian ambassador Rita Klimova is back at her Washington home after six weeks of chemotherapy for acute leukemia, a cancer of the white blood cells, according to embassy spokesman Daniel Vesely. Klimova, the first ambassador to Washington in President Vaclav Havel's post-communist government, was diagnosed with the condition in June and was treated at Johns Hopkins University Hospital in Baltimore. She has recovered enough to begin maintaining office hours in early January, but it won't be a full schedule; "she will be available for meetings and consultations," said Vesely.

Arena Fund-Raiser Leaving Arena Stage's fund-raiser Elspeth Udvarhe lyi will be leaving the theater at the end of the current season to join the Baltimore Museum of Art in the same capacity, according to Producing Director Zelda Fichandler. In the announcement yesterday, Fichandler said that "Arena Stage and I have been fortunate to have worked with Elspeth for the past 11 years," and praised her "extraordinary vision, hard work, and unabashed enthusiasm." Udvarhelyi, who joined Arena in 1980 as its first full-time fund-raiser, said it was time to move on. "My decision has been long in the making," she said, "and I feel that it has been made at the most opportune time for Arena."

Burt Lancaster Leaves Hospital Actor Burt Lancaster, who suffered a stroke two weeks ago, has left a Los Angeles hospital and will undergo extensive physical and speech therapy, a spokeswoman said yesterday. It will be several weeks before doctors will know "how soon he'll be working again," a spokeswoman for the 77-year-old Academy Award-winning actor said.