WASHINGTON — The White House argued on Tuesday that the “unique circumstances” presented by the opportunity to return Sgt. Bowe Bergdahl gave President Obama the authority to lawfully bypass a federal statute requiring the Pentagon to notify Congress a month before he transferred the five Taliban detainees necessary to complete the deal.

But the White House was forced by turns to defend its decision not to notify Congress and to send important aides to apologize to angry lawmakers who said they were left out of the decision.

On Wednesday, administration officials denied they had apologized to leading senators for the decision not to inform them ahead of the prisoner exchange. They said they had only expressed regret that on Saturday, as the exchange took place, they reached staff members but not the senators themselves. The White House insists that its decision not to conduct an advance consultation fell within the president’s executive powers, no matter how the statute read.

A timeline of the negotiations with the Taliban, provided by the White House, made clear that it knew an imminent transfer was possible by mid-May, roughly two weeks before it took place. And officials familiar with the sequence of events said it was a desire to keep the talks secret for fear that any disclosure would scuttle the negotiations — and perhaps a reluctance to re-engage with Democratic and Republican members of Congress who were critical of the proposed swap in 2011 and early 2012 — that motivated the White House decision.