Top officials for the N.B.A. and the players union will meet Sunday night in a final, and unexpected, attempt to resolve the lockout before regular-season games are lost, according to a person briefed on the meeting. The meeting will involve the primary negotiators for each side — Commissioner David Stern and the deputy commissioner Adam Silver for the league, with the union represented by its president, Derek Fisher, and its executive director, Billy Hunter. The season is scheduled to start Nov. 1., but Stern said last week that he would be forced to cancel the first two weeks of regular-season games on Monday if the sides did not have a breakthrough at the bargaining table. They have not met since then, with the N.B.A. insisting it will not move beyond the 50-50 split in league revenues that Stern proposed last Tuesday. The union rejected that stance, saying it would not resume talks with any preconditions. The players have been earning 57 percent of basketball-related income and offered to reduce their share to an annual average of 53 percent, which would be a pay cut of at least $120 million a year. Dropping to 50-50 split would mean a pay cut of at least $280 million a year, notwithstanding any increase in league revenues. It is not clear whether the league has moved off of its 50-50 proposal, or whether the union has softened its insistence on receiving 53 percent of league revenues in a new collective bargaining agreement. It is also possible that the sides are negotiating other, structural issues in an attempt to move forward. Union officials said last week they wanted to restart talks on other issues, like the salary cap, but the precondition of a 50-50 split precluded a return to negotiating. Silver indicated Friday that the league was "prepared to continue negotiating over the many other issues that remain open" — like the salary-cap system, the luxury tax and the length of contracts. The N.B.A. lost games in 1998-99, when a bitter lockout reduced the season to 50 games. The league did not open play until Feb. 6 that season.