WASHINGTON, Feb 27 (Reuters) - U.S. senators asked Defense Secretary Robert Gates on Wednesday to launch a broad investigation into Pentagon acquisitions of wartime equipment, including armored vehicles, saying its methods may be putting U.S. troops at risk.

In a letter to Gates, a bipartisan group of four lawmakers -- including the chairmen of the Senate foreign relations and intelligence committees -- said Defense Department acquisition practices may not be working well enough to protect U.S. troops in Iraq and Afghanistan against the most sophisticated roadside bombs.

A Defense Department spokesman had no immediate comment. The letter was dated Wednesday and posted on the Web site of the public advocacy group, Project on Government Oversight.

"We urge you to conduct a thorough and comprehensive evaluation of all of our wartime acquisition processes, in all of the services and at the joint level," said the letter.

It was signed by Sen. Kit Bond, a Missouri Republican, and Democrats Joseph Biden of Delaware, John Rockefeller of West Virginia and Edward Kennedy of Massachusetts.

Biden and Rockefeller chair the Senate foreign relations and intelligence committees, respectively.

Their letter said Mine Resistant Ambush Protected (MRAP) vehicles with special protection to safeguard troops from armor-piercing roadside bombs are still months from delivery despite repeated requests dating to Feb., 17, 2005.

MRAPS, which the Pentagon has begun shipping to combat areas in large numbers, are designed to withstand the blast of most roadside bombs.

But the vehicles offer little protection against explosively formed penetrators, or EFPs, which are capable of piercing heavy armor. U.S. officials say the deadliest EFPS have come from Iran, a charge Tehran denies.

"In addition, the Army's delays in initially fielding better body armor, up-armored Humvees and MRAPs appear to be symptoms of the same problems," the letter said.

Separately, the Defense Department inspector general's office issued a statement saying it was reviewing two Pentagon reports including a Navy audit that point to problems commanders in Iraq have had requesting MRAPs and other items. (Reporting by David Morgan, editing by Stuart Grudgings)

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