WASHINGTON - A congressional committee on Thursday asked for an investigation into a counterterrorism database software upgrade that it says is months behind schedule, millions over budget and would actually be less capable than the U.S. government terrorist tracking system it is meant to replace.

At issue is Railhead, a software upgrade to the Terrorist Identities Datamart Environment, which is a vast database of names that feeds the nation's terrorist watch list. It is meant to help analysts "connect the dots" between known or suspected terrorists and their contacts, potential targets and safe houses. As of January, the database contained 500,000 names. The upgrade was supposed to be completed by the end of this year.

But the House Science and Technology investigations and oversight subcommittee said Thursday that the program "has been imploding for more than one year," citing internal program documents and e-mails obtained by the committee.

"The program appears to be on the brink of collapse after an estimated half-billion dollars in taxpayer funding has been spent on it," said subcommittee chairman Rep. Brad Miller, D-N.C., in a statement issued Thursday.

Miller said the "majority" of more than 800 private contractors from dozens of companies working on Railhead have been laid off, and the National Counterterrorism Center "drastically curtailed" the program last week and may shut it down completely.

Spokesman Carl Kropf of the counterterrorism center declined immediate comment.

Miller sent a letter to the national intelligence director's inspector general requesting an investigation.

The committee also says "Railhead insiders" allege the government paid the Boeing Co. $200 million to retrofit the company's Herndon, Va., office with security upgrades so top secret software work could be performed there and then leased the office space from Boeing. A Boeing spokesman could not be immediately reached for comment.

The committee investigation also found problems with the existing terrorist database. It says 40 percent of suspect names and addresses contained in CIA cables that should be entered into the database are never entered.