America discovered Christopher Columbus last night, a nice twist considering the explorer's 15th-century maps identified this part of the world only as an empty void in which "here be dragons."

Things have changed a lot since then but there are still dragons, and Washington's were out in force. Some showed up at the Kennedy Center to see a condensed version of the mini-series bearing Columbus' name, which CBS will air in two segments May 5 and 6.

Others were guests at an Italian Embassy dinner for Prime Minister Bettino Craxi and his wife, Anna Maria, given by Ambassador Rinaldo Petrignani and his wife, Anne Merete.

Craxi, winding up two days of talks here with President Reagan and key members of his administration, was in an ebullient mood. Earlier in the day he became the first Italian prime minister in 34 years to address a joint session of Congress.

He was also the first Socialist leader from Italy to do so. And at the dinner, one plaudit came from Sen. Malcolm Wallop (R-Wyo.), who thought it remarkable to find a European socialist so articulately in favor of the European Community's defense. "You expect that from a Thatcher or a Kohl, people of a more conservative persuasion, but not of someone like Craxi. He may be in the vanguard of others to come from the European left."

Earlier, at the Kennedy Center, Sen. Larry Pressler (R-S.D.) emphasized the pragmatic in talking about Craxi's day. "They bent the rules for him," Pressler said, referring to the prime minister's appearance on the Hill. "They did it for Margaret Thatcher but they've turned down Argentina and they don't know what they're going to do yet about India. If they let one prime minister address Congress, then they're afraid they have to let them all."

Craxi has endorsed U.S. plans for its Star Wars research, and at the Kennedy Center told the crowd that Columbus' spirit lives today in the exploration of outer space.

"Science and courage are at the basis of our civilization. To make headway is an obligation," he said, speaking through an interpreter.

Later, at the embassy dinner, Craxi left the speeches to his foreign minister, Giulio Andreotti, and to Defense Secretary Caspar Weinberger. But when they had finished, he popped up from his table and proposed a champagne toast to President Reagan, who did not attend.

Craxi got his share of kudos from the guests, who included a sizable Senate and House turnout such as senators Gary Hart (D-Colo.), William Cohen (R-Maine.), Paul Laxalt (R-Nev.), William Roth Jr. (R-Del.), Dennis DeConcini (D-Ariz.), Patrick Leahy (D-Vt.), Alfonse D'Amato (R-N.Y.); and representatives Dante Fascell (D-Fla.) and William Broomfield (R-Mich.).

Others in the crowd of 150 were Commerce Secretary Malcolm Baldrige, Health and Human Services Secretary Margaret Heckler, Agriculture Secretary John Block, Attorney General Edwin Meese III, Deputy Secretary of Defense Kenneth W. Dam, Ambassador Maxwell Rabb, Motion Picture Association of America chief Jack Valenti, former ambassadors John Volpe and Claire Boothe Luce and the Common Market's Sir Roy Denman.

Heckler was accompanied by Boeing lobbyist Jack Pierce, who was seated at a nearby table for the dinner of roast pigeon. All the smokers at the table waited for Pierce to light up, which he did surreptiously because the Health and Human Services secretary has asked him not to smoke at dinner parties they attend. He kept his ashtray hidden.

Heckler flies to Rome tomorrow to sign an agreement between Italy and the United States on vision research.

ABC's Barbara Walters came with Lorimar Productions chairman Merv Adelson. His company has produced the six-hour mini-series "Christopher Columbus," as well as prime-time soaps "Dallas," "Falcon Crest" and "Knots Landing."

"Columbus" director Alberto Lattuada told dinner partners of a 3 1/2-day Mediterrean cruise with 50 Italian television critics, who were previewing the series, which debuts today in Italy. "They were trapped, but so was I."

Before dinner, Weinberger took some bows for his crackdown on General Dynamics. "We're perfectly willing to pay for proper charges but we're not willing to pay for improper charges," said Weinberger of his decision to freeze administrative payments to the defense contractors until questions are answered about overhead costs.

"I yield to no man in my admiration of dogs," he said, "but I don't want to have the taxpayers pay to stable them."

DeConcini was one congratulating Weinberger, going back to do it after he made a pitch for the secretary's support on a new air wing that would patrol U.S.-Mexican borders for drug smugglers.

"He was noncommittal though he indicated he supports the concept," the senator said of Weinberger's response to his arm-twisting.

Block said President Reagan's predicted veto of the farm bill put an end once and for all to "a lot of political game-playing."

"It's been pure nonsense, you know," Block went on. "Nobody can tell me the Democrats are all for farmers and the Republicans aren't. That what I call political game-playing."