The speech that President Raul Alfonsin of Argentina is scheduled to make to a joint meeting of Congress this week is a high honor, one not bestowed lightly or easily.

It takes energetic lobbying by the guest government, the White House and the State Department to achieve it.

There have been only 27 such speeches by foreign dignitaries in the 24 years since John F. Kennedy became president. Leaders from Mexico, Ireland and France have spoken three times each, but most nations never have sent anyone to the exalted podium in the House of Representatives.

The decision of who gets to address the assemblage of the House and Senate, the Cabinet, the Supreme Court and the other cream of the city's politerati -- and who does not -- involves all the intricacies of foreign policy, national interest, Capitol Hill politics and White House strategy rolled into one prickly subject. Few are willing to be quoted on how it works.

On paper, "the request goes from the foreign government to the speaker of the House, who issues the invitation," said Selwa Roosevelt, director of the State Department's Office of Protocol. Christopher Mathews, spokesman for House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.), said formal requests from the White House are the ones that usually are honored.

In practice, according to several sources, everybody has a veto. The White House, the National Security Council, the State Department and party leaders in both houses of Congress have to agree that the speech would be a good idea. That is why there are so few speeches.

"The American system is really pluralistic," said a foreign diplomat whose government's request was successful. "There's no central command. There were all sorts of groups we had to convince."

Weeks before a dignitary's impending visit is publicly announced, the foreign government's ambassador and his staff are mentioning to guests and contacts how nice it would be if the visitor got to make "the speech." Could the friend make a couple of calls?

The result is a three-aspirin headache for the administration. "Nobody wants to be the one to say no, so it bounces back and forth between the White House and State," said a knowledgeable administration official. "Most of the time they the foreign governments have the grace not to ask."

But many do. Too many. "If you started having all of them who ask , they'd become passe. You wouldn't have good attendance . . . and that could be a real embarrassment," said a State Department official whose job includes making some of the calls.

President Jimmy Carter said no to everybody except Prime Minister Pierre Trudeau of Canada, whose February 1977 speech to a joint congressional meeting was the only one of the Carter term.

Traditionally, Mexico and Canada are so honored as next-door neighbors and friends whenever their leaders arrive. Otherwise, "it has to be a special reason," the administration official said.

After the Carter years, Princess Beatrix of the Netherlands ended the drought in 1982 because it was the 200th anniversary of U.S. diplomatic relations with her country and because her mother and grandmother also had made "the speech" generations ago. West German President Karl Carstens spoke in 1983 and British Prime Minister Margaret Thatcher this year on similar 200th anniversaries, the official said.

But Italy's Prime Minister Bettino Craxi spoke this year partly because Irish Prime Minister Garret Fitzgerald did last year, and their respective voting blocs keep track of such things. French leaders get the nod "because we're traditionally trying to impress the French," one congressional official joked.

Although Alfonsin's appearance reflects a genuine desire to honor a democratically elected president who ousted the generals of Argentina, it also reflects a desire to avoid the charge that Americans always favor the British as they did in the Falklands-Malvinas Islands conflict between Argentina and Great Britain in 1982, the sources agreed.

A well-known Argentine here indicated that the Argentines now are one up. The last time an Argentine made "the speech" was when President Arturo Frondizi appeared in 1959, he said, but Britain's last speech before Thatcher's was Winston Churchill's appearance in 1952.

Lobbying clearly is the key. As for all the other countries whose hopes of speaking have gone unfulfilled, he said, "Probably they didn't try hard enough."