Questions arose about Lynn's suitability after President Barack Obama imposed tough new ethics rules Jan. 21 to keep lobbyists out of top government posts. Lynn was a vice president and lobbyist for the defense giant Raytheon.

Hours before the OMB decision, four government watchdog organizations urged the Senate Armed Services Committee to reject Lynn for the No. 2 post at the Pentagon.

Even top Obama aides conceded Lynn's appointment would require a waiver from new rules that prohibit lobbyists from serving in agencies they have lobbied in the previous two years.

Lynn was senior vice president for government operations and strategy at defense giant Raytheon and a registered Raytheon lobbyist until last July.

His nomination "causes an impossible conflict," officials from four organizations said in a letter to Sens. Carl Levin and John McCain, the chairman and senior Republican on the Armed Services Committee.

But in a late afternoon statement, Levin said the waiver to Obama's ethics rules "has removed an obstacle to the confirmation of Bill Lynn to be deputy secretary of defense."

The Armed Services Committee will still insist that Lynn "recuse himself for a period of a year from any decisions involving his prior employer unless specifically authorized to participate by an appropriate ethics official," Levin said. "I support Mr. Lynn's nomination."

McCain remained skeptical. "Before I can determine whether to support his nomination," he said, "I intend to ask him to clarify for the record what matters and decisions will require his recusal."

McCain said he applauded Obama's new, more stringent ethics rules, and "had hoped he would not find it necessary to waive them so soon."

The watchdog organizations argued that waiving the new ethics rule is "a frontal violation" of reforms intended to keep lobbyists out of top government posts.

But confirming him without a waiver would mean he must recuse himself from matters affecting Raytheon. The fifth-largest U.S. defense company sells $18 billion worth of missiles, radars, sensors, munitions, space systems and other technology to the U.S. military and other government agencies annually.

Sitting out decisions that involve Raytheon "would make it impossible for [Lynn] to effectively serve" as deputy defense secretary, the four said. They are the directors of the Project on Government Oversight, Citizens for Responsibility and Ethics in Washington, the Government Accountability Project and the legislative representative of Public Citizen.

In an effort to reduce the influence of special interests and restore the public's faith in government, Obama proclaimed new ethics rules Jan. 21 that he said are the toughest in U.S. history.

"If you are a lobbyist entering my administration, you will not be able to work on matters you lobbied on, or in the agencies you lobbied during the previous two years," Obama said. "When you leave government, you will not be able to lobby my administration for as long as I am president."

Later, White House spokesman Robert Gibbs said Obama's ethics rules included a provision for waivers if they are approved by the White House Counsel. He said Lynn "is superbly qualified" for the deputy defense secretary job.

Defense Secretary Robert Gates told reporters he asked for an exception to be made for Lynn because he is the best candidate for the job.

But the rising flap over Lynn and lobbying has raised doubts on the Armed Services Committee.

Sen. Claire McCaskill, D-Mo., said Lynn represents "a strong example" of the "industry-government executive revolving door phenomenon" in which industry executives take Pentagon jobs and are perceived to benefit the companies they once worked for at taxpayers' expense.

"To be frank, the way DoD does business with defense contractors must change because the status quo is unacceptable," McCaskill said. "In my limited interaction with Mr. Lynn to date, I have not sensed a strong commitment to this type of change, although I understand he has communicated such a commitment to others with great vigor."

Even so, McCaskill said she would not object to Lynn's confirmation. An aide said McCaskill is giving Lynn "the benefit of the doubt because he is giving up a lot to return to government service, suggesting a lot about his character."