Senate Democratic leaders, eyeing a shot at controlling the White House in just six months, are shutting the door on approving many of President Bush’s picks for federal boards and commissions — a move that while far from unprecedented has Republicans bristling.

The virtual lockdown comes after 18 months of on-and-off-again negotiating between Majority Leader Harry Reid (D-Nev.) and White House officials over federal appointments, which cover the ambassadorships to the more incendiary jobs at the Justice Department. The logjam has never cleared, but at times the two sides have agreed to push through a block of appointments, usually leading up to a Senate recess period.

Yet with just a few months before a new president is elected, Democrats and Republicans alike acknowledge that majority Democrats have lost incentive to clear many of Bush’s nominees, particularly if doing so would ensure Republican majorities on commissions or boards beyond the current president’s term. Reid and other Democratic leaders are banking on either Democratic Sen. Barack Obama (Ill.) or Sen. Hillary Rodham Clinton (N.Y.) winning the White House and making his or her own installments come January.

“It is traditional that at the end of the administration, the party opposite to that in the White House will not move nominations to boards and commissions where to do so would put that body in Republican hands into a new administration,” a senior Democratic Senate aide said. “Where control is not an issue, we will keep confirming.”

The move certainly isn’t unheard of, yet Republicans are fuming that many of their home-state choices for those unfilled positions are being held hostage. As one White House official said, “this is strictly the wait game” for Reid.

“He kind of made the decision to do as little as possible and run out the clock,” Sen. John Thune (R-S.D.) said. “It’s not a good precedent for a government to function. But he seems intent or content with leaving with a lot of those positions vacant.”

Sen. Judd Gregg (R-N.H.) agreed, saying that despite Democratic protests to the contrary, Republicans didn’t act similarly when they controlled Congress. He charged that Senate Democrats have had a “much more aggressive policy” in denying Bush’s appointees.

“It’s a mean-spirited attempt to do a tit for tat with the administration,” Gregg said. “It underscores the level of dislike between the Congress and this president, and it’s so deep and visceral on the Democratic side.”

But Reid and Senate Democrats have argued that they have been more collegial toward Bush and his selections than when a Democrat controlled the White House against a GOP Senate majority. Reid last week advanced a number of stalled ambassadorships, for instance, which Democrats say is a sign that they continue to work toward advancing noncontroversial Bush appointments.

“Sen. Reid has been far more generous in his treatment of Republicans than they treated Democrats in recent years,” Reid spokesman Jim Manley said. “We’ll continue to process these types of nominees as quickly as possible. But we’re not going to confirm people and put these boards in Republican hands as we get ready for a Democratic administration next year.”

Sen. Ben Nelson (Neb.), a moderate Democrat who helped lead the “Gang of 14” that ended the 2006 standoff over confirmation of Bush’s judicial nominations, said that while Republicans may be unhappy with the pace of confirmations, with no sensitive positions left unfilled and Bush’s term ending, it is not unexpected.

That is especially true, he said, for largely patronage positions or appointments that come with terms that last into the next administration.

As dozens of executive branch slots remain in the queue, a deal to confirm at least three federal appellate court nominees is on track for Memorial Day, and negotiations are in the works to unlock the stalemate over four vacancies at the Federal Election Commission.

Emily Lawrimore, a White House spokeswoman, said Bush has continued to press for action on pending nominations and has said, “These highly qualified individuals are making real sacrifices and they should not be treated like political pawns.” Lawrimore also reminded that “it would be wise to remember that it sets a bad precedent for future administrations” for the Senate to stall on the scores of nominees.

One pair of those appointments recently led to a standoff between Reid and Senate GOP Conference Chairman Lamar Alexander (Tenn.) over two of Bush’s reappointments to the board of directors for the Tennessee Valley Authority, the eight-state public works project developed under the New Deal. While the panel itself rarely sparks controversy, it has ignited a feud between the two Senators, with Alexander calling Reid “irresponsible” for slow-walking otherwise qualified nominees simply because a new president is around the corner.

Alexander is particularly upset about the reappointment of William Graves, a Christian Methodist Episcopal Church bishop and self-described Democrat who also served as a co-chairman of Bush’s 2004 campaign in Tennessee. “I don’t question other Senators’ motivations, but I do question their actions. There’s no explanation for it,” he said.

Reid, for his part, has protested the imbalance on the authority and takes issue with Bush having full ownership of the nine-member body. Republicans expanded the board from three to nine in 2004. On the TVA before its expansion, Manley said: “It had a long tradition of bipartisan representation in the past. In the new iteration, all the picks went to the president.”

That TVA spat aside, Sen. Bob Menendez (D-N.J.) said it’s time to begin considering the needs and desires of the next administration. “At this stage, the reality is the next administration, Republican or Democrat, is going to have to govern for the next four years. … It is only right that he or she should be able to select” whom they would like to fill open positions, particularly those that will last for several years, Menendez said.

Nelson also noted that Bush’s low approval ratings have undercut his — and Senate Republicans’ — arguments for approving noncritical nominees.

“Your standing in terms of approval ratings can shade your level of success,” he said.