The USO celebrated its 50th anniversary last night with a gala dinner for 1,000 guests and dignitaries at the Omni Shoreham. It was a happy evening celebrating half a century of "caring, service and love" for American service personnel, and yet unhappy too, in that once again salving the psychological stresses of impending war is a growth industry. USO officials announced they will soon have three service centers open in the Persian Gulf region, one inside Saudi Arabia itself, with others in Dubai and Bahrain.

Boxing champion Thomas "Hit Man" Hearns, who recently did a handshake tour in Saudi Arabia under USO auspices and pronounced it "great," was there last night. "To be picked to go and help the morale of the troops, I got a great deal out of it. It made me feel really good," he said. And the troops loved him too, according to a short film on USO tours shown last night. There was Hearns, doing a little pickup match with one of the soldiers, surrounded by cheering onlookers.

"The Saudis don't have the same idea about a good time as we do," said Rep. John D. Dingell (D-Mich.), explaining why comedian Steve Martin had to confine himself to a "handshake tour" and why Bob Hope's act will be scaled down. Of course, he added, "Those military personnel are not over there for shows."

Would that they were.

"It is the USO challenge to minister to the deep human needs resulting from the hardships" American service personnel are suffering in the gulf region today as they await a possible war, said World USO President Chapman B. Cox. He added that "Bob Hope is going for Christmas," and said in a private interview that Hope will be entertaining as well as greeting troops inside Saudi Arabia.

USO officials made it clear last night that the details are not yet nailed down, one of the principal difficulties being the "sensitivities" of the conservative Moslem culture to such standard USO show fare as dancing girls. Hope, 87, has been entertaining American forces abroad at Christmas since 1941 with gala shows including plenty of starlets and irreverent humor.

"Hope can't do his normal show because of Saudi restraints," said Executive Vice President Richard Henry. Kevin McCarthy, executive producer of the USO's entertainment programs, said, "We don't have a cast from Bob" yet, but that when one arrives, it will be submitted to the Defense Department for approval, which in turn will make sure that the Saudis are not offended.

But the emphasis last night was on the positive -- on the more than 150 USO centers around the world where lonely service personnel can get "a smile and a hot cup of coffee," on the American corporations who have donated millions of dollars to provide off-duty services for the troops deployed on Operation Desert Shield, and on certain key figures on the American landscape who have made the USO a vital concern.

August A. Busch III, who runs the world's largest brewery, Anheuser-Busch, out in St. Louis, received the USO's Great American award last night for contributions totaling $3.5 million during the past five years. Busch came to the rescue when the USO was between wars and in managerial disarray in 1985, and kept with the task until the organization was again healthy. "It's our way of saying 'thank you' to the men and women who defend our country," he said last night.

An Outstanding Civic Achievement award was given to advertising executive Keith Reinhard, who during that same period donated ad and public relations services that generated $25 million for the privately funded charity organization. And President Bush's father, Prescott Bush, was honored posthumously with a Christmas Award for having spearheaded the stunning $32 million fund-raising drive that launched the United Service Organizations in 1941 on the eve of America's entry into World War II.

William Prescott Bush -- the president's nephew -- was on hand to accept this award, recalling his grandfather as "a tall, handsome, successful man with a great sense of humor and a love of life." He also recalled that the elder Bush was a devoted member of a barbershop quartet from 1926 to 1962.