NEW YORK — NFL labor negotiations took yet another surprising turn late yesterday when the league and union agreed to postpone free agency another 72 hours, giving the sides more time to try to reach agreement on a contract extension.

NFL spokesman Greg Aiello said the delay would give owners a chance to consider the union's latest proposal during a meeting tomorrow in Dallas.

Talks broke off earlier in the day, leaving dozens of veterans in danger of becoming salary-cap casualties before free agency was supposed to begin today at a minute after midnight.

The breakdown in talks was typical of the topsy-turvy negotiations, so far: Just when things seemed darkest, they got back on track; and when it appeared a deal could be struck, talks fell apart.

The union broke off yesterday's session.

"The talks ended after the NFL gave us a proposal which provided a percentage of revenues for the players which would be less than they received over the last 12 years," said Gene Upshaw, executive director of the NFL Players Association. "After suggesting we extend the waiver deadline from six o'clock to 10 this evening, they gave us a new proposal which was worse than their prior offer. Quite naturally, we rejected that proposal and saw no need to continue meeting."

But Harold Henderson, the NFL's executive vice president for labor relations, said the union rejected a proposal that would have added $577 million for players in 2006 compared to 2005 and $1.5 billion in the six years of the extension. "It's an unfortunate situation for the players, the fans and the league," Henderson said.

A mere four hours later, things were fluid again.

After a conference call between owners and league officials, including commissioner Paul Tagliabue, the league announced yet another extension — the second 72-hour respite in free agency, which originally was to start Friday.

"The NFL and the NFL Players Association have agreed to extend the start of the 2006 league year for 72 hours — until 12:01 a.m., EST, Thursday, March 9 — in order to allow the NFL clubs to meet in Dallas tomorrow to consider the NFL Players Association's offer," the NFL said.

Shortly afterward, Upshaw said: "The NFL negotiators called us tonight after our negotiations broke off to indicate that they will take our complete package to the owners for an approval vote on Tuesday. We have therefore agreed to extend the free agency deadline until midnight Wednesday in order to provide time for that vote to be accomplished. It was the NFL's previous rejection of our proposal earlier this evening that caused the talks to break down."

The deadline for teams to be under the salary cap also was pushed back. Though cuts had already started, the cap extension changed things.

Teams are trying to squeeze under a salary cap of $94.5 million. If a deal is reached, the cap could go as much as 10 million higher — in other words, allowing teams to keep some of the players.

These negotiations were by far the most difficult since the NFL and the union first agreed to free agency and a salary cap in 1992, ending years of labor unrest that included player strikes in 1982 and 1987. The contract has been extended several times since then, most of the time with ease.