WASHINGTON — Congressional researchers say the military doesn't have reliable estimates of how contaminated its test and training ranges are, nor how much it would cost to decontaminate them.

In fact, the Pentagon may not even really know such basic information as the size or number of its current and former ranges.

Without that information, Congress and base closure commissions will have a difficult time weighing "the potential costs versus benefits of closing operational ranges or entire installations," according to a new report by the U.S. General Accounting Office, a research arm of Congress.

Utah is home to several military ranges, most notably the Rhode Island-size Dugway Proving Ground operated by the Army and the similarly vast Utah Test and Training Range operated by Hill Air Force Base.

Both could figure in the next round of base closures scheduled for next year. Hill has faced, but narrowly escaped, closure in the last two rounds — helped by its possession of the UTTR. Dugway was proposed for closure in 1995 but escaped when other states would not allow transfer of some of the chemical and biological work conducted there.

The military recently prepared, as ordered by Congress, some inventories of ranges and estimates of costs to clean up contamination there.

In a review of that information, the GAO warns that the Defense Department's resulting "estimate that it would cost between $16 billion and $165 billion to clean up unexploded ordnance, discarded military munitions and munitions constituents on operational ranges is questionable."

One major problem, it said, is the military truly does not have a clear picture of how many ranges exist and how big they are. The GAO said different arms of the military used different criteria, assumptions and methods in their inventories, which "raise questions about the reliability" of comparisons and cost estimates made using them.

It said the Pentagon reported 10,444 operational ranges covering 24.6 million acres nationally in a 2003 inventory. But a 2004 inventory listed 353 range complexes and 172 individual ranges on 26 million acres worldwide.

Sometimes the same arm of the military reported different numbers in separate inventories for the same ranges, it said.

For example, one inventory said the Marines' Camp Lejeune, N.C., has 95,872 acres of rangeland, while a more recent inventory says it has 152,000 acres, even though the entire installation covers 153,000 acres.

Another example is that the Marines' Camp Pendleton, Calif., was listed having 39,084 acres of range in one inventory, and 114,000 acres in a more recent one — a threefold increase.