Turning to a trusted former adviser, Senate Majority Leader Bill Frist (R-Tenn.) has hired a new chief of staff, Lee Rawls, who had served as Frist’s senior adviser in the late 1990s and now is the top aide to FBI Director Robert Mueller.

Rawls will begin his new job April 28 after the spring recess, replacing outgoing Chief of Staff Mitch Bainwol, according to Republican sources.

“Anybody who knows Lee knows him as someone who is extraordinarily capable,” said one veteran GOP aide.

In going with Rawls, Frist chose someone with decades of experience in Washington and with whom he has a close trust — but also someone who has no experience working in Senate Republican leadership.

An aide said Frist is happy to bring on board both a “Capitol Hill veteran” and someone he has worked closely with in the past.

Since the 1970s Rawls has bounced between the Senate and the Justice Department in various roles, with a few short stints in the private sector.

From 1996 to 2000, he was administrative assistant in Frist’s personal office, helping lay the groundwork for Frist’s re-election in 2000 and his jump into leadership as chairman of the National Republican Senatorial Committee for the 2002 cycle. But he left the Senator in 2000 to work as the FBI’s special counsel; he later became Mueller’s chief of staff.

In the first Bush administration, Rawls was the Justice Department’s top liaison with Capitol Hill, serving as the assistant attorney general for legislative affairs from 1990 to 1992.

Rawls did not return a call Friday at his FBI office seeking comment.

Rawls’ hiring is also another move sure to ingratiate Frist with one of the chamber’s top Old Bulls, Energy and Natural Resources Chairman Pete Domenici (R-N.M.). Rawls served two stints as chief of staff to Domenici, first in the late 1970s and then again from 1982 to 1985.

Since taking over as Majority Leader in December, Frist has now selected three former Domenici staffers as his top aides. In addition to Rawls, Frist hired William Hoagland, Domenici’s longtime budget adviser, and Bob Stevenson, the New Mexican’s former top press aide.

Bainwol’s departure was long expected, as he had already opened his own consulting and media relations firm after serving as Frist’s executive director at the NRSC.

After Republicans ousted Sen. Trent Lott (R-Miss.) as leader because of fallout from his remarks at former Sen. Strom Thurmond’s (R-S.C.) birthday party, Frist coaxed Bainwol into coming aboard the leadership team to help set up the shop. When he leaves Frist in late April Bainwol will reopen his firm and continue to be an important outside adviser to the Majority Leader.

Rawls will have to hit the ground running because this spring is likely to witness a major partisan fight over the shape and direction of President Bush’s domestic agenda, with the Senate serving as the prime battleground.

Frist’s first three months on the job have brought mixed results. His supporters note that the Senate passed the omnibus appropriations measure in January to clear up leftover matters from the 107th Congress; approved a ban on a so-called partial-birth abortion procedure considered critical to conservative voters; and passed a budget resolution out of the chamber before the end of March, something the Democrats didn’t even attempt to do in 2002.

“In a matter of three months we’ve done as much as some Congresses have done in a year,” said one GOP aide.

However, Democrats have been privately crowing about a few high-profile GOP losses in recent weeks. The circuit court nomination of Miguel Estrada continues to be mired in a so-far-unbreakable Democratic filibuster, Republicans lost a key vote on drilling for oil in an Alaskan wildlife refuge after a misunderstanding with a couple of moderates, and Bush’s tax cut was slashed in half after an initial victory on the issue.

With such a narrow margin for victory or defeat, Frist will need all the help he can get from Rawls and his other top staffers in the months ahead.

“Any time you have a 51-49 Senate, you have a tough job,” an aide said.