Richard C. Holbrooke, the new U.S. ambassador to the United Nations, has eschewed the formal $30,000-a-month ambassador's residence at the Waldorf Astoria. But that hasn't stopped his 27-year-old executive assistant, R.P. Eddy, from checking into the luxury hotel suite where Secretary of State Madeleine K. Albright and Energy Secretary Bill Richardson lived during their terms as ambassador.

A spokesman for the U.S. mission to the United Nations said Eddy was allowed to stay at the Waldorf to save the government $200 a night for a separate Manhattan hotel room for him. In exchange for the quarters, Eddy has agreed to forgo his $80 a day housing allowance, the spokesman said.

The residence has mostly been vacant since Richardson left New York to head the Energy Department last September. Peter Burleigh, acting head of the U.S. mission for the past year, used the Waldorf for official functions but did not live there.

Holbrooke, who has worked as an investment banker on Wall Street between diplomatic posts, owns a private home in New York. He plans to use the Waldorf for entertaining foreign dignitaries, the spokesman said.

Republicans on Capitol Hill have "casually" begun to consider whether to make a stink about the cost of two residences for Holbrooke, one congressional aide said. "How much more will it cost the taxpayer to have Holbrooke live in his house?" the aide asked. "Although there is no additional rent, there are additional costs like security that have to be met."

The high cost of the Waldorf residence, used since 1949, has long been a source of irritation in Washington. At the birth of the United Nations, a rich benefactor offered to give the United States a town house on the East River for the top American diplomat, said David Birnbaum, a former senior U.S. official at the U.N. But the United States turned it down, worried that it would cost too much to maintain. It was given instead to the U.N. secretary general.

Asked whether he thought it was appropriate for a relatively junior staffer to be handed the keys to the government's most sought-after diplomatic residence, Birnbaum said: "I'm very pragmatic. Rather than have a place unused, I'd rather see it used. What do we get out of the place if it's vacant?"

Eddy said through a spokesman that he intends to live at the Waldorf only until he can find his own apartment. Holbrooke left yesterday for an official visit to the Balkans and was unavailable for comment.

Holbrooke was sworn in as ambassador this week after a 14-month delay in his confirmation by the Senate, due to an ethics investigation and "holds" placed on the nomination by a few Republican senators as bargaining chips in disputes with the Clinton administration.