WASHINGTON - The image of Sen. James Webb (D., Va.) gaveling the Senate in and out of session in 30 seconds has become a staple of wry political commentary lately. But the senator's lonely vigil represents more than Washington gamesmanship. In a way, it marks a shift in the balance of power between the executive and legislative branches.

The proper line has been at issue throughout President Bush's tenure, with the White House determinedly expanding its reach through such means as signing statements that effectively invalidate parts of legislation, and even now the threat to cancel thousands of congressional earmarks. But this may be the first time in a while that the balance has tilted back toward the other end of Pennsylvania Avenue.

That's because Senate Majority Leader Harry M. Reid (D., Nev.) is holding these pro forma sessions to keep Bush from making recess appointments. Under the Constitution, the president is empowered to make temporary appointments when the Senate is out of session, a provision intended to keep government going in the days when lawmakers had to ride horseback to come to town. In modern times, presidents have used breaks to install nominees who otherwise would not be confirmed.

Reid decided that enough was enough and held this sort of pro forma session over Thanksgiving, then decided to do it again after talks with White House Chief of Staff Joshua B. Bolten broke down.

In this case, Reid said, it came down down to one nominee: Steven G. Bradbury for assistant attorney general. As acting head of the Justice Department's Office of Legal Counsel in 2005, Bradbury signed two secret memos authorizing harsh CIA interrogation techniques on terror suspects - techniques that critics deem torture.

Reid said "there is no chance" Bradbury would be confirmed, yet Bush refused to rule out giving him a recess appointment.

Reid said that he had offered to confirm 60 stalled Republican nominees and eight Democrats to various positions if Bush would give up Bradbury, but that Bush refused.

"Think about this," Reid said last week. "Because the president wants one person whom we cannot get out of the Judiciary Committee, he is willing to hold everything up. It doesn't sound like much of a compromise to me."

Reid sent through those nominees anyway because "I am not going to meet stubbornness with stubbornness."

The White House, unsurprisingly, views it differently. From its perspective, the Senate warped the equation by routinely holding up even unobjectionable nominees for political reasons or no discernible reason at all. More than 165 nominations are pending, White House officials said, so the recess appointment becomes a necessary corrective tool to fill vacancies and keep government moving.

"The Senate's role is to advise and consent, not attack and condemn," said White House spokesman Tony Fratto. "This harassment of nominees turns away qualified people who would otherwise want to serve their country. This is just another example of the breakdown of Congress under this leadership."

Associate Senate historian Donald A. Ritchie said that, as far as he knew, this was the first time the Senate had held pro forma meetings after a session for the express purpose of blocking appointments.

At this rate, the Senate presumably will do so until Bush leaves office, effectively taking away his recess appointment power. The question is whether this becomes a permanent shift.

Ritchie said it set a precedent mainly for "when the president and Senate leadership are this far apart, and when it's so late in an administration that the president has given up hope of having certain nominees ever confirmed."