Relations with many of their countries haven't always been easy in Ronald Reagan's seven years as president. But nobody in the white tie-national dress crowd of foreign envoys would have missed Reagan's diplomatic swan song for the world.

"I figured it was my last chance to see him before he leaves the White House," explained one ambassador at Reagan's sixth -- and final -- party last night for some 150 members of the diplomatic corps. "Next year you'll have a new president."

Reagan, with his wife Nancy, who wore a black Galanos gown covered with glittering swirls of silver, received their guests in the Blue Room, posing with each for a souvenir photo. Diplomats were too diplomatic to try talking business with their host.

"Of course not. We will say what we have to say through regular channels," said Panama's Ambassador Juan B. Sosa, though he described himself as "furious" over attacks here against Gen. Manuel Antonio Noriega. The Panamanian strongman was indicted last week by two federal grand juries in Florida on charges of taking bribes from drug traffickers.

Just back from Panama, where he was summoned on Sunday, Sosa said, "There's a political motive behind all this and we're going to be answering it. We feel that there is an effort by sectors in this country, together with the opposition in Panama, to create an atmosphere to change our government."

Soviet Ambassador Yuri Dubinin merely smiled when asked whether he talked about anything serious when he shook Reagan's hand. Then in a burst of excitement Dubinin asked, "But what do you think about Mr. Gorbachev's statement on Afghanistan?"

Soviet leader Mikhail Gorbachev announced on Monday the Soviets' plans to start withdrawing Soviet troops from Afghanistan in mid-May. Dubinin said last night that the withdrawal could begin even sooner, "if the Geneva talks have sufficient time to finish and to sign an agreement."

He called Gorbachev's announcement "a breakthrough in all regional problems in general. The Soviet Union is making big efforts to achieve it."

Another topic for many of the diplomats was the American political process. Nobody speculated on who might win the presidency, and in the wake of Monday night's caucuses in Iowa, at least one ambassador, Senegal's Falilou Kane, was drawing no conclusions at all.

"I'm a sportsman," he said, "and I know you can't win one game in the first three minutes."

Switzerland's Klaus Jacobi and his wife Johanna dashed in long enough to see the Reagans, then rushed home, where Vice President Jean Pascal Delamuraz was waiting. Jacobi said he had invited Vice President Bush to meet Delamuraz, who automatically becomes president next year, but that Bush is campaigning in New Hampshire.

"Vice President Bush has to fight very hard to be president next year, but not Vice President Delamuraz," he said.

The Reagans' first diplomatic reception, also white tie, was in 1981, shortly after he took office. A succession of parties followed, some black tie, some business suits, and at least one spontaneously coatless. That was on a steamy July day in 1985 when Nancy Reagan stood in for Reagan, who had undergone cancer surgery.

In 1987, a year Nancy Reagan has described as "terrible," the Reagans skipped the diplomatic party altogether.

Last night, diplomats who had national dress wore it instead of white tie and those in black tie sported their medals and ribbons. It was probably a tossup between the ambassadors of Japan and Norway as to who had the most decorations, although U.S. Ambassador to the United Nations Vernon Walters was right up there with a chestful of military ribbons.

"I've probably been in more wars than any of them," said Walters of the crowd.

Secretary of State George Shultz said he bought his white tie and tails nearly 20 years ago when he was secretary of labor in Richard Nixon's Cabinet. "And it still fits," he said, adjusting his jacket.