Sen. Barry Goldwater (R-Ariz.) successfully underwent triple-bypass heart surgery yesterday at St. Joseph's Hospital in Phoenix.

Dr. Ted Diethrich, Goldwater's physician, said the senator "couldn't be better, regardless of his age." Goldwater is 73. Diethrich said at a news conference that two of Goldwater's arteries had been 90 percent blocked and a third was 85 percent blocked. "Before the surgery, the senator was definitely in a life-threatening situation," Diethrich said. He said no heart muscle damage was found.

Goldwater is expected to remain in intensive care for three days and should be released from the hospital in 10 days.

Sheik Mohamed Fassi, who has been in the public eye for the past nine months for his philanthropic donations to ailing American cities, apparently has left the country.

"He's gone," said Gabriel De La Rota, president and owner of Jet Charter in Miami, the firm that rented a 707 jet to the sheik. "We flew him to Riyadh Saudi Arabia , and as far as I know, he's still there. I don't think he's going to be an important man around Miami anymore."

The sheik reportedly took his children to Riyadh over the weekend to see his sick mother, according to Special Master Mallory Horton, despite a court order that his children not be taken out of Dade County until settlement of a divorce and custody suit brought by his estranged wife, Dena. Horton was appointed to handle the case by Circuit Judge Jack Turner. Yesterday he cited the sheik in contempt of court for violating the order.

Attorneys for Fassi said they are convinced the sheik, who has been gone since last Sunday, will return to the country.

A settlement was reached yesterday in New York in a suit filed by author J.D. Salinger accusing a man of impersonating the reclusive novelist and short-story writer and passing off his own writings as Salinger's.

In the agreement, the defendant, Steven Kunes of Manhattan, agreed to be permanently enjoined from representing by any means that he is associated with or ever met Salinger. The agreement also bars Kunes from exhibiting, transmitting or distributing documents, writing or statements attributed to Salinger. Kunes also is required to collect and turn over any offending documents or writings to be destroyed.

In return, Salinger agreed to withdraw his claims for unspecified monetary damages and legal costs.

In filing the action Sept. 30, the author claimed Kunes tried to sell People magazine "a completely fictitious interview with Salinger." Salinger did not appear in court.

More than 300 browsers and buyers were on hand last night for a benefit preview of the Mount Vernon College Antiques Show, which began a three-day show today at the Washington Hilton.

The $30 per person that guests paid last night will go to the Mount Vernon College Scholarship Fund. In return, guests were treated to cocktails, music and antiques displayed by 86 dealers from around the country.

Among the antique lovers was cochairman of the show, Theo Hayes, who is married to Steven Hayes, a direct descendent of Rutherford B. Hayes; Henry Strong, chairman of the board of trustees of Mount Vernon College; Mr. and Mrs. Florenz Ourisman; Barbara Allbritton, wife of businessman Joesph L. Allbritton; Ann Page, chair of the Antiques Show Committee, and interior decorator Bob Waldron.

Most of the guests wore black and white, everybody wore hard hats and the tablecloths wore workmen's footprints when the American Society of Interior Designers Potomac Chapter had a preview dinner last night at the new D.C. Design Center. The center is expected to open in January at Fourth and D streets SW.

The annual awards were presented at the box supper, with centerpieces of flowers growing out of rubble. Antony Childs was voted ASID's annual designer of distinction award by the membership. Design competition awards went to Keith Babcock for first place in residential interior category with Larry Horn as runner-up. William L. Wilkoff won the commercial interior first place with Gail Biddison as runner-up. The Smithsonian Associates won the ASID Potomac Award for its programs on interior design. The ASID Medalist Award for service was presented to Milo Hoots.

END NOTES: The arrival of Britain's Princess Anne at Nairobi airport yesterday sparked a scuffle between police and photographers jockeying for a clearer view. Anne is to spend three days in Kenya, the fourth stop of her African tour on behalf of a children's charity . . . Polish film director Andrzej Wajda has been chosen by the Onassis Foundation as the recipient of its Athinai Prize for his "contribution to freedom" . . . Singer Rick Nelson and his wife were divorced Wednesday in Los Angeles. Nelson and Kristin Harmon Nelson were separated in 1977 after 14 years of marriage.