NEW YORK (AP) _ Maybe it was the mind-numbing heat that had Mayor Rudolph Giuliani briefly thinking the emperor and empress of Japan were from Italy.

''You are among friends in New York City and in America,'' the mayor told Emperor Akihito and Empress Michiko as he toasted them during a dinner at the Metropolitan Museum of Art on Wednesday night.

''The friendship between Italy ... ,'' Giuliani started to say as the audience laughed. ''Italy? Japan and the United States,'' he continued, ''is a strong and a very deep one, and one that you will enhance by your visit throughout the United States.''

Then Giuliani uttered something in Japanese that left Akihito looking puzzled. Members of the emperor's entourage said they could not understand what the mayor said.

Gov. Mario Cuomo said Japan and the United States are ''two great peoples.''

''We wish the best that can be wished for between friends,'' he added.

Earlier, the mayor and his wife, Donna Hanover Giuliani, had met the emperor and empress in the presidential suite of the Waldorf-Astoria Hotel.

Giuliani profusely apologized for how the hazy heat had obscured the city's famous skyline after the royal couple landed Wednesday as part of their 16-day U.S. tour. The visit is described by Japanese officials as intended to promote good will between two countries whose economic partnership is strained by trade disputes.

Giuliani, carrying a gift in a blue wrapper, welcomed Akihito with a handshake. And noting the record-tying 96-degree heat and the haze that blanketed the city, he said: ''Hopefully the fog will lift and tomorrow it will be bright and sunny.''

Akihito responded, ''I look forward to seeing the skyline.''

Akihito and Michiko greeted guests in the Met's Charles Engelhard Court, with its collection of American art, before dining on beef Wellington with a celebrity-studded, black-tie gathering of about 400 in the Temple of Dendur exhibit.

Banker David Rockefeller and Arthur Ochs Sulzberger, chairman of The New York Times Co., were co-chairmen of the dinner welcoming committee.

The guest list included a clutch of former prime ministers - Sir Edward Heath of Britain, Jacques Chirac of France, Amintore Fanfani of Italy, Chancellor Helmut Schmidt of West Germany and Yasuhiro Nakasone and Kiichi Miyazawa of Japan.

Other notables were former Mayor David Dinkins, violinist Isaac Stern, designer Hanae Mori, economist Paul Samuelson and entrepreneur Donald Trump.

Akihito, 60, grew to gray-haired middle age before assuming Japan's ''Chrysanthemum Throne'' in 1989 after the death of his father, Hirohito.

Hirohito, Japan's longest-reigning sovereign, was once photographed on a visit to Disneyland wearing a Mickey Mouse watch, but for the most part he was a remote figure who appeared rarely in public.

His son is an outgoing type who was tutored in English as a youth and has tried to demystify the royal family, whose lives have long been jealously protected by the tradition-steeped Imperial Household Agency.