David Stern led the NBA through drug problems and work stoppages. Now his league faces the stigma of a point-shaving scandal involving a referee.

The NBA acknowledged yesterday that the FBI is investigating Tim Donaghy for betting on games, including ones in which he officiated.

According to a law enforcement official, authorities are examining whether the referee made calls to affect the point spread in games on which he or associates had wagered over the past two seasons.

The referee had a gambling problem and was approached by low-level mob associates through an acquaintance, said the official, who spoke to the AP on condition of anonymity.

Donaghy is perhaps best-known previously as one of the referees in the 2004 game at Detroit that ended with Indiana Pacers players fighting with Pistons fans, among the biggest black marks in league history.

This could top it.

"We would like to assure our fans that no amount of effort, time or personnel is being spared to assist in this investigation, to bring to justice an individual who has betrayed the most sacred trust in professional sports, and to take the necessary steps to protect against this ever happening again," Stern said in a statement.

Donaghy officiated 68 games in the 2005-06 season and 63 games in 2006-07, according to the Elias Sports Bureau. He also worked 20 playoff games, including five last season — Pistons-Magic on April 23; Warriors-Mavericks on April 27; Suns-Lakers on April 29; Nets-Raptors on May 4; and Spurs-Suns on May 12.

The National Basketball Referees Association did not return calls for a statement, and Donaghy reportedly has resigned from the league.

A woman came to the door of the Bradenton, Fla. home where Donaghy lives and shouted through the door: "We have no comment."

Defense attorney John Lauro confirmed Donaghy is under investigation but refused to comment.

Stern's statement said the FBI is investigating allegations a "single" referee bet on basketball. But the law enforcement official, who requested anonymity because he was not authorized to discuss the ongoing case, said other arrests are expected.

Those studying Donaghy's games might have noticed some trends.

When the home team was favored by 0 to 4 1/2 points, it went 5-12 against the spread in games officiated by Donaghy this season, according to Covers.com, a Web site that tracks referee trends. Home underdogs were 1-7 against the spread when it was 5 to 9.5 points.

Donaghy was part of a crew working the Heat-Knicks game in New York in February when the Knicks shot 39 free throws to the Heat's eight, technical fouls were called on Heat coach Pat Riley and assistant Ron Rothstein, and the Knicks won by six. New York was favored by 4 1/2.

NBA players in Las Vegas for USA Basketball minicamp were surprised and disappointed to learn of the accusations.

"As a competitor, as hard as I play, it is disappointing, definitely," LeBron James said.

Pistons guard Chauncey Billups said he was surprised to learn of Donaghy's situation.

"I think everybody had the same kind of reaction whether you played in the league or just a regular citizen," Billups said.

The investigation first was reported yesterday by the New York Post.

"I'm shocked, terribly shocked," said Gary Benson, an NBA official for 17 years who retired two years ago because of knee problems. "Those are people that you work with and that you literally — you spend more time with those people than you do with your family."