By CARL HULSE

WASHINGTON — C. Boyden Gray, the former White House counsel and ambassador, is among the conservative lawyers urging the Supreme Court to severely constrain the Obama administration’s ability to fill executive branch vacancies during a Senate recess. Mr. Gray is exceptionally well versed in the subject, having received his own recess appointment in 2006.

“I have been on both sides of this issue,” said Mr. Gray, who was named ambassador to the European Union without Senate confirmation by President George W. Bush on Jan. 17 of that year. “The one for myself was a holiday recess. It was a real recess, and I don’t think there was any doubt about it.”

What constitutes a real recess is just one of the issues as the fight over Senate confirmations moves to the Supreme Court. On Monday, the court will hear arguments in the administration’s challenge of an appeals court ruling that would tremendously restrict a president’s power to, as the Constitution allows, “fill up all vacancies that may happen during the recess of the Senate.”

Since George Washington’s time, presidents have relied on the clause to fill vacancies, with some exploiting it as a founding loophole to circumvent the Senate’s role of advice and consent. The Senate struggle over nominations forced the issue to a head in the courts through the legal challenge of President Obama’s decision to install nominees on the National Labor Relations Board via recess appointment in January 2012.

The story has a remarkable number of twists, turns and role reversals, even for a convoluted Washington brawl. Besides Mr. Gray, at least two other conservative lawyers who are pushing for restraints were put on the federal Legal Services Corporation board by recess appointment — during the Reagan administration. A Congressional Research Service review in February found those three appointments and hundreds of others since 1981 might have been invalid under the court ruling being reviewed by the Supreme Court and supported by the former recess appointees.

Defenders of the administration say the fact that Mr. Gray and others who received recess appointments now contest the power is evidence that the conservative complaint is more about the Obama administration’s ability to fill vacancies.

“It helps show how aggressive conservatives have been in the past in arguing for strong executive power and utilizing the recess appointments clause,” said Doug Kendall, the president of the Constitutional Accountability Center. “The conservative case for a broad recess appointments power is strong, and the wails expressed by conservatives over President Obama’s utilization of the clause are crocodile tears.”

Adding to the atmosphere, the lawyer who will represent Senate Republicans at the Supreme Court is Miguel Estrada, whose nomination to the United States Court of Appeals for the District of Columbia Circuit by President Bush was blocked by Senate Democrats in 2003, touching off the current nomination fight.

It was that same court that ruled against the Obama administration on the National Labor Relations Board recess appointments. One of the chief arguments for ruling the appointments invalid was that the Senate was not in recess at the time since it was holding pro forma sessions every few days. That tactic was actually first engineered by Senator Harry Reid, the Democratic majority leader, to thwart President Bush from making any more recess appointments.

Mr. Reid played another card in the nomination fight in late November when he orchestrated the move by Senate Democrats to make a simple majority sufficient to overcome a filibuster on nominations except for the Supreme Court. That action has, for the moment, limited the need for Mr. Obama to make more recess appointments since he can win confirmation of nominees by simple majority as long as Senate Democrats are willing to use the required Senate floor time.

“The rules change has taken the steam out of the issue,” Senator Charles E. Schumer of New York, the No. 3 Senate Democrat, said about the recess dispute.

But if Senate Republicans were to win the majority next year – not an inconceivable notion – Mr. Obama could again be forced to use Senate recesses to install contentious nominees, and a Supreme Court ruling against recess appointments could limit his options.

In the case now known as National Labor Relations Board v. Noel Canning, No. 12-1281, the federal appeals court delivered a stunningly narrow definition of a recess appointment. It said that such appointments could be made only during a declared recess between Senate sessions and that the only vacancies that could be filled had to occur during that recess.

It was a very strict interpretation of the constitutional clause written two centuries ago when there were long breaks between sessions because of travel and communication difficulties. The ruling went far beyond how the power of recess appointments has been interpreted in modern times, when presidents have often taken the opportunity, even during short breaks, to make appointments.

The administration appealed the appeals court ruling, saying in its brief that “the practice of making an appointment during a recess to fill a vacancy that predated the recess is so well and long established that it is impossible to determine how many such appointments have occurred in the last 190 years.”

Even critics of the appointments concede that the ruling could have gone too far. But they say the administration overreached with the N.L.R.B. appointments by making them during a period when the Senate was meeting every three days in pro forma sessions. Conservatives see it as another example of the Obama administration’s abusing its executive authority.

“This is part of a larger battle,” said William J. Olson, who filed a brief supporting the appeals court decision on behalf of Citizen United and other conservative organizations. “Presidents want to be able to avoid the role of the Senate.”

Mr. Olson says his own recess appointment to the Legal Services Corporation board of directors by President Ronald Reagan on Dec. 31, 1981, met the test of coming between sessions. It is a bit unclear as to whether the seat he filled can be considered to have come vacant during the same recess – the other test. “It never came up at the time,” he said.

Mr. Gray, who wrote a brief on behalf of the Competitive Enterprise Institute and others who challenged a recess appointment to the Consumer Financial Protection Bureau, said he expected the Supreme Court to stray from the appeals court stance but impose some limits.

“I don’t think the Supreme Court is going to go as far,” he said. “I think they will say there has to be a real recess, that it can’t just be lunch hour.”