One balmy night last week, Washington's mighty diplomatic and political community gathered to fete Henry Kissinger. The hosts, Tom and Joan Braden, had invited both the British and Argentine ambassadors, before the Falkland Islands crisis began.

Britain's influential Sir Nicholas Henderson canceled at the last minute, saying he had to work late. Later that evening, however, he did attend the even more exclusive black-tie dinner for Kissinger at the home of AFL-CIO President Lane Kirkland.

Argentina's Esteban Takacs, a new name in the diplomatic corps, was not invited to the Kirkland dinner. His shining hour came during cocktails at the Bradens'.

"I hope I remember what he looks like," said one prominent Washington woman a few minutes before Takacs arrived. But moments later, she was standing with him, smiling and questioning. He was sought after by the powerful throughout the vast house. Kissinger. Assistant Secretary of State Lawrence Eagleburger. Former assistant secretary of state William D. Rogers. Reporters.

"If you want to be famous and stay in the news, you have to sit close to me," the Argentine ambassador jokingly whispered to Kissinger. The two men laughed.

As the world grimly monitors the Falkland Islands drama, starring Great Britain and Argentina, the two rival ambassadors are playing out antithetical roles here: Henderson, rumpled and donnish, but tall in diplomatic stature; and Takacs, immaculately turned out and strikingly handsome, but low on the diplomatic totem pole.

The usually prosaic routine of an ambassador--afternoon teas, speeches to Rotary Clubs, obligatory dinners--has been transformed for both into marathon phone calls to their foreign ministers, intense meetings with Secretary of State Alexander Haig, and back-to-back media interviews.

However, their personal styles of scrambling through this crisis constrast sharply. Each man's particular ambassadorial style reflects the professional and political position the Falklands crisis has put him in.

Henderson, ubiquitous on the social circuit in quieter times, is now picking and choosing his public exposure carefully. A career diplomat from a world power, Henderson, who has been assigned to Washington since 1979, is accustomed to dealing in lofty circles. He has always had easy access to Alexander Haig, for instance.

Takacs' access to Haig began with the crisis three weeks ago. The Argentine ambassador, who has been here only six months, has suddenly become a social and media darling, frequently seen at parties and granting dozens of interviews. On a single day last week five film crews filed through his office: units from ABC News, "Today," "Good Morning America," and two Washington stations. And he has established a reputation for being outspoken.

"I feel as if I'm watching a science fiction movie," he said, in his lilting Spanish accent, of the crisis. "The idea of the British fleet moving toward the islands is like something out of last century. This whole thing has gotten blown out of proportion. Don't you think?"

Henderson has said he is careful to avoid Takacs around town. But Takacs, a successful businessman turned ambassador, thinks the two men should speak: stature and status quo versus ambition and confrontation.

Henderson refused four interview requests over a period of eight days for this article. "The ambassador is prepared in principle to help . . . but it's physically impossible," offered a spokesman.

Henderson, known to his friends as Nicko, has been staying close to home and to the powerful friends he has made in his 30-year career. On April 1, the night before the Falklands crisis became public, for example, he entertained some friends for his birthday: Vice President George Bush and Barbara Bush, White House deputy chief of staff Michael Deaver, Joan and Tom Braden, journalist Alfred Friendly Jr. and his wife, Pie, and a handful of others.

It was clubby and cozy. But tense. Everyone took turns going to the phone. Deaver played the piano. The vice president toasted Henderson, offering sympathy over the crisis. Two days later, Henderson publicly criticized U.S. representative to the United Nations Jeane Kirkpatrick for attending an April 2 dinner in her honor at the Argentine Embassy.

"Parties," said Takacs, now smiling boldly, "are part of my working style . . . they give you a chance to communicate and stay in touch. They are less pleasure and more work."

"Nicko is not going to go out to cocktail parties and dinners when his country is almost in a war," says Joan Braden, a friend of Henderson.

"I insist that this is not an invasion," said Takacs, earlier this week sitting in a formal red velvet chair at his embassy. "I don't like that word. We didn't invade. We retook the islands. We considered these islands ours. The British have no right at all to be there."

Takacs has delivered this speech over and over since Argentina took the islands April 1. He is charming, self-assured and the perfect picture of gray pin stripes and pride. Gray streaks run through his meticulously styled hair.

Takacs presented his diplomatic papers to President Reagan last October, arriving here with his wife and three children after a five-year stint as ambassador to Canada. "He did such a good job there," said OAS secretary general Alejandro Orfila, himself a former Argentine ambassador to the United States, "that he was asked to come to the United States."

"I feel that I have to inform the American public about our views, about our position, how we see things," Takacs said. "I understand that it's not easy for them to understand our position . . . because they feel they were for a long time allies with the British . There is a natural friendship."

Takacs is particularly concerned with what he calls "active propaganda" being passed by the British, and that concern has become a part of his regular appeal to the media.

"There is a special and real propaganda effort being made by the British trying to give the impression to the media that Argentina is an ally of the Soviet Union," he said. "It's aimed to disbalance the American perception of the Argentine issue. So I'm talking about that a lot--informing the public as well that what we do have with the Soviet Union is a commercial relationship . . ."

He doesn't understand, he said, why the British are reacting the way they are.

"Dignity?" he asked, leaning foward. "Over a question of national dignity, the British are going to go in and kill 10 or 15 thousand Argentine soldiers?"

These days, when he's not explaining to the American people, he is on the phone with his foreign minister, Nicanor Costa Mendez, or assistant secretary of state Thomas Enders. Sometimes a dozen times a day. He says he's buying a beeper this week so he can get away from his desk more often.

"I've been too busy to even pay courtesy calls on all my colleagues since I've been here . . ." he said. "I must do that."

Even the British ambassador?

"I don't see any difficulty in talking with him whatsoever," he smiled. "After all, we don't believe this issue should be an unsolved thing.