WASHINGTON — Deputy Attorney General Paul McNulty said yesterday that he will resign, the highest-ranking Bush administration casualty in the furor over the firing of U.S. attorneys.

Mr. McNulty, who has served 18 months as the Justice Department’s second-in-command, announced his plans at a closed-door meeting of U.S. attorneys in San Antonio. He told them he would remain at the department until late summer or until the Senate approves a successor, aides said.

He also sent a one-page letter of resignation to Attorney General Gonzales, whose own job has been put in jeopardy by the firings and their aftermath.

“The financial realities of collegeage children and two decades of public service lead me to a long overdue transition in my career,” Mr. McNulty said in the letter, which did not mention the firings controversy. Neither did Mr. Gonzales, in a responding statement that praised Mr. McNulty as “a dynamic and thoughtful leader.”

“Paul is an outstanding public servant and a fine attorney who has been valued here at the department, by me and so many others, as both a colleague and a friend,” Mr. Gonzales said.

Mr. McNulty has been considering leaving for months, and aides said he never intended to serve more than two years as deputy attorney general. But his ultimate decision to step down, the aides said, was hastened by anger at being linked to the prosecutors’ purge that Congress is investigating to determine if eight U.S. attorneys were fired for political reasons. The aides spoke on condition of anonymity because they were not authorized to talk publicly about Mr. McNulty’s decision.

Mr. McNulty also irked Mr. Gonzales by testifying in February that at least one of the fired prosecutors was ordered to make way for a protégé of Karl Rove, President Bush’s chief political adviser.