WASHINGTON (AP) _ Eighty-one congressmen are demanding the removal of the director of the Smithsonian's Air and Space Museum. They complain that he refuses to make changes in a forthcoming exhibit of the fuselage of the Enola Gay, the B-29 that dropped the first atom bomb on Japan.

But Smithsonian Secretary I. Michael Heyman is standing behind the director, Martin Harwit. ``The secretary has said he will not be letting him go,'' said Smithsonian spokesman Linda St. Thomas.

In a letter to Heyman, 68 Republicans and 13 Democrats cited Harwit's decision to lower the exhibit's estimate of the number of Americans who would have perished in an invasion of Japan to 63,000 _ not the 229,000 originally estimated.

Harwit acted on the advice of historian Barton Bernstein of Stanford University, who said he had restudied World War II records. The bombing of Hiroshima and Nagasaki in August 1945 brought Japan's swift surrender, making an invasion unnecessary.

The controversy over the exhibit has gone on for a year. Veterans groups said the museum, on the influence of ``revisionist historians,'' had made it seem that Japan was the victim of racist American aggression.

In a letter, the congressmen wrote that negotiations on ``a mutually acceptable script'' had borne fruit but Harwit's ``continuing defiance and disregard for needed improvements to the exhibit has put this tenuous agreement into disarray.''

They called his actions ``a slap in the face to all the parties who contributed their time and expertise in creating an exhibit that best reflects the contributions that all Americans made to the culmination of World War II.''

Among those signing the letter were Reps. Dick Armey of Texas, the Republican majority leader; Tom DeLay of Texas, the GOP whip; John Boehner of Ohio, chairman of the House Republican Conference, and Bob Stump of Arizona, chairman of the Veterans' Affairs Committee.

Sen. Ted Stevens, R-Alaska, chairman of the Senate Rules Committee, who flew in the Flying Tigers in China, said he planned Senate hearings on the issue. House hearings are also planned.

The controversy is to be discussed Monday by the Smithsonian board of regents, governing body of the institution. The exhibit is scheduled to open in May.