WASHINGTON (AP) _ Sen. Alfonse D'Amato said Thursday he is blocking confirmation of President Bush's nominee to head the Urban Mass Transit Administration to force a promise that the agency will study New York City's transit troubles.

D'Amato, R-N.Y., put a hold on the nomination of Brian W. Clymer, of Media, Pa., preventing a confirmation vote by the full Senate.

Clymer, a certified public accountant, is a former director of the Southeastern Pennsylvania Transportation Authority.

D'Amato apparently is not the only senator objecting to Clymer's nomination. According to reports published last month, Clymer's nomination was blocked by other senators because of a questionable link to the scandal- plagued Department of Housing and Urban Development.

Clymer's accounting firm reportedly received no-bid contracts to audit the books of a Pennsylvania developer that received a grant from the Department of Housing and Urban Development.

Clymer was not available for comment late Thursday, according to Richard Centner, an UMTA spokesman. Clymer has been filling the administrator's job since Alfred Dellibovi left the job to became deputy HUD secretary.

Last April, Dellibovi announced UMTA would investigate safety at the MTA, which has been plagued by fires, doors opening on moving trains, crashes and other hazards.

But on Thursday, the senator said ''virtually no progress has been made on this probe and it appears to be going nowhere.''