Embattled U.S. Attorney Frank McNamara resigned Monday, saying the work of federal prosecutors was "too important" to be disrupted by the controversy surrounding him.

"The work here is too important to be sidetracked by any controversy," McNamara, 41, told a news conference."I am deeply grateful to former President Reagan for my appointment. I've thoroughly enjoyed working here these last two years and now is the time for Frank McNamara to return to private practice as a lawyer."

McNamara, who was appointed by Reagan in 1986, came under fire over allegations that he had lied when he reported seeing his predecessor, William Weld, smoke marijuana.

McNamara, the subject of a Justice Department probe, later acknowledged that he himself had smoked marijuana. He has also been criticized for his handling of the investigation into alleged extortion in the construction of 75 State St., a downtown skyscraper.

Twenty-eight of the attorneys in his office had reportedly called on Attorney General Richard Thornburgh to fire McNamara, but Thorn-burgh hesitated for fear McNamara would file an unprecedented suit against the Justice Department, The Boston Globe reported.