(Releads with quotes from spokesman, adds defense official; previous BAGHDAD)

WASHINGTON, Aug 31 (Reuters) - A military airplane carrying four members of the U.S. Congress came under fire over Iraq on Thursday but the plane was not hit and no one was hurt, a spokesman for one of the lawmakers said on Friday.

The C-130 cargo aircraft conducted evasive maneuvers after a nighttime takeoff from Baghdad, said Ken Lundberg, spokesman for Sen. Mel Martinez of Florida, who was on the plane.

In addition to Martinez, the plane was carrying fellow Republican Sens. Richard Shelby of Alabama and James Inhofe of Oklahoma, and Alabama Rep. Robert "Bud" Cramer, a Democrat.

Lundberg said Martinez had been told three rocket-propelled grenades were fired at the plane. But a senior U.S. defense official in Washington said small arms fire appeared to have been responsible.

"He (Martinez) had just taken his body armor off and was getting ready to snooze," Lundberg said the senator told him. "Then there was a flash of light, and the plane started banking in different directions."

"The whole incident was over in three to five minutes," Lundberg said, and the aircraft flew on to Amman, Jordan.

A statement from U.S.-led forces in Iraq said the plane "observed surface-to-air fire" upon departure from Baghdad and dispensed flares and conducted "standard evasive maneuvers."

The fire originated several miles from the plane's location, the defense official in Washington said, speaking on condition of anonymity as U.S. forces in Baghdad were officially responsible for commenting on the incident.

"They (the crew) did all the right things, they took all the appropriate precautions, but it appears they were at an altitude that did not put them at any danger from the type of small arms fire that they received," the official said.

The lawmakers had spent the day in Baghdad and were briefed by U.S. Iraq commander Gen. David Petraeus.

A number of U.S. lawmakers have been visiting Baghdad ahead of a series of pivotal reports to be delivered to Congress in coming weeks on the security and political situation in Iraq.

(Reporting by Susan Cornwell and Andrew Gray in Washington and Dean Yates in Baghdad, editing by Vicki Allen; Reuters Messaging: susan.cornwell.reuters.com@reuters.net, +1 202 898 8300))

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