WASHINGTON – The FBI, concerned that terrorists could use lasers as weapons, is investigating why laser beams were directed into the cockpits of six commercial airliners since Christmas. Laser beams can temporarily blind or disorient pilots and possibly cause a plane to crash.

A federal law enforcement official speaking on condition of anonymity said that the bureau is looking into one incident in Cleveland, two in Colorado Springs, Colo., and three others. Separately, law enforcement officials confirmed that a laser was aimed at a jet in Teterboro, N.J., on Wednesday, and another at a plane landing in Medford, Ore., on Christmas night.

Though the official said there is no evidence of a plot or terrorist activity, pilots are troubled by the incidents. The FBI earlier this month warned of the possibility that terrorists might use the devices as weapons.

“It’s not some kid,” said Paul Rancatore, a pilot and deputy chairman of the security committee for the Allied Pilots Association. “It’s too organized.”

Loren Thompson, who teaches military technology at Georgetown University, called it a “rather worrisome development,” though he said experts would be more puzzled than alarmed.

“What we’re talking about is a fairly powerful visible light laser that has the ability to lock onto a fast-moving aircraft,” Mr. Thompson said. “That’s not the sort of thing you pick up at a military surplus store.”

Mr. Thompson said a piece of equipment that could do the things the FBI suspects would be “fairly expensive and fairly sophisticated….It sounds like an organized effort to cause airline accidents.”

Law enforcement officials, though, say they have no evidence of such an effort and that the lasers in question are readily available. Further, they say they’ve had reports of similar incidents since the technology became popular.

However, a memo sent to law enforcement agencies recently by the FBI and the Homeland Security Department says there is evidence that terrorists have explored using lasers as weapons, though there’s no intelligence that indicates they might use them in America. Pilots and safety officials have long been concerned about the dangers of laser light shows, which have caused temporary eye injuries to several pilots over the last decade.

Most recently, a pilot for Delta Air Lines reported an eye injury from a laser beamed into the cockpit while approaching the Salt Lake City airport in September. The plane landed safely.

An FAA-commissioned study in June concluded that “a laser attack could be quickly deployed and withdrawn, leaving no obvious collateral damage or projectile residue, and would be difficult to detect and defend against.”