The FBI said Friday it is investigating apparent sabotage of O-rings destined for space shuttle booster rockets, a problem a NASA official said may have been motivated by a company incentive program.

A "very small number" of O-rings that appeared to have been deliberately cut were discovered by the manufacturer, HydraPak Inc., in June, and the incident was immediately reported to the FBI, NASA, and Morton Thiokol, said James Dockstader, company vice president of operations.He said a check showed none of the flawed seals was shipped to Morton Thiokol, which produces the booster rockets in Utah.

J.R. Thompson, director of NASA's Marshall Space Flight Center in Huntsville, Ala., said some HydraPak employees are suspected of damaging the O-rings to receive bonuses awarded to workers who found defects.

"My understanding is they tightened internal final inspection, incentivized it or came up with some kind of program to make sure (no flawed O-rings) got out," Thompson told The Huntsville Times Friday.

"After HydraPak set up this internal thing, perhaps some employees may have been taking advantage of it. That's what's suspected. Whether it's a fact, I don't know. We're treating it as an internal HydraPak thing," he said.

Under the incentive plan, workers reportedly were awarded points for finding defects missed in previous inspections. When they accumulated enough points, they received a cash bonus. However, the system was eliminated after the defects appeared, The Times reported.

Dockstader denied, however, that HydraPak employees were given a cash incentive and said Thompson was "either misinformed or misquoted."

He did confirm a Times report that in addition to the O-rings that were deliberately cut, several others were left in a curing oven believed to have been left deliberately on a hotter-than-normal setting.

Former HydraPak inspector Cathy Crocker told KSL-TV Friday that she discovered three O-rings with slash marks as early as May, but management was unable to determine who was responsible.

After more cuts were found, Crocker said she was asked to take a lie detector test.

"I did. I had nothing to hide. I liked my job at that company. I took the test and I failed it. They came in and took me off my inspection," she said.

Crocker said that when cuts continued to surface in some O-rings, she was moved to a filing job and was asked by management to resign.

Dockstader said no employees were fired as a result of the investigations, but he would not say whether any were disciplined.

A faulty O-ring that allowed super-hot gases to escape and ignite the shuttle's exterior fuel tank was blamed by a presidential commission for the Jan. 28, 1986, Challenger disaster, which killed the craft's seven-member crew and grounded the nation's shuttle program.

NASA is expected next week to set a date for the launch of Discovery, the first post-Challenger mission. The agency currently has an internal target of Sept. 29.