WASHINGTON (AP) _ When Timothy McVeigh blew up the Oklahoma City federal building, the government had a TOW antitank missile stowed in a locker several floors above the daycare center.

The missile, about 3 feet long, actually had an inert warhead and only a small amount of rocket fuel, and the government says it did not contribute to the massive explosion that day. Instead, it tumbled into the rubble of the Alfred P. Murrah Federal Building.

But its discovery prompted an evacuation that slowed rescue efforts April 19, 1995, in part because the missile had been marked as live ordinance to make it look believable to the targets of a planned law enforcement sting, according to documents obtained by The Associated Press.

``Tow Missile recovered from A.P. Murrah Building,'' states an Oklahoma County sheriff's department evidence form showing the missile was removed from the rubble by the department's bomb squad and examined by military ordinance experts.

Oklahoma City emergency personnel records show the rescue site evacuation lasted 44 minutes.

``People were scrambling in every direction,'' recalled Sgt. William Grimsley of the Oklahoma County sheriff's department bomb squad, who helped remove the missile during the evacuation. ``From the crate, we knew it was some kind of a missile. We were told to get it out of there and get it out of there as fast as we could.''

The missile was the subject of a lengthy FBI investigation and also was examined by a local grand jury in Oklahoma, according to documents and interviews, but its existence has remained mostly a secret to the public _ except for a handful of conspiracy theorists and government critics.

``There was a gag order at the time, we just didn't talk about it at all. It was an ongoing investigation,'' Grimsley explained.

McVeigh was convicted and later executed for the truck bomb blast that killed 168 people, including 19 children _ most of them in a day-care center on the second floor.

Though a sidelight in the Oklahoma City drama, the missile's unexpected appearance in the rubble of a federal building frequented by civilians _ including children _ raises broader safety issues, experts say.

``We have no idea of what the potential dangers are in federal buildings because there is no methodology'' for the General Services Administration, the government's landlord, to independently review what is stored in every building, said John Culbertson, a former congressional aide to expelled Rep. James Traficant, D-Ohio.

Culbertson investigated the Oklahoma City building and other federal building safety issues and testified before a House subcommittee.

The GSA says its security procedures have changed greatly since 1995. The changes ``include extensive exchange of information with local, state and federal law-enforcement organizations, designing federal buildings to incorporate security measures and using magnetometers, X-ray machines and other innovations, some not visible to the public,'' GSA spokeswoman Viki Reath said.

Just last summer, GSA implemented a new regulation requiring federal agencies to seek its authorization before bringing ``hazardous explosive or combustible materials'' into federal buildings.

Still, the TOW missile is among a growing number of recent examples of weaponry, ordinance and other potentially dangerous materials that have been involved in incidents in government buildings.

In December, an FBI agent suffered severe burns on his hands, arm and abdomen when a stun grenade accidentally exploded in a federal building in Buffalo, N.Y. Witnesses said the explosion shook the building and caused smoky haze to drift through the complex.

And shortly after the Sept. 11 attacks, authorities divulged that a government office building that collapsed in a fiery heap near the World Trade Center had stored thousand of gallons of diesel fuel in tanks just above the ground floor. Investigators have examined whether the fuel could have contributed to the fire and collapse, and some insurance companies have sued the Port Authority of New York and New Jersey for storing the fuel there.

The federal building in Baltimore was evacuated in 1997 when pepper gas was discharged, overcoming several workers.

Some potential perils have been known by the government for more than a decade.

In 1987, a fire inside an FBI crime laboratory in Washington set off ordinance stored casually in a cabinet. ``The detonation of ordinance stored in the lower area of the cabinet occurred late in the fire as the heat level approached the floor,'' an FBI investigative report said.

That report states that among the items to detonate were two rocket-propelled grenades and 30 Soviet-made detonating fuses.

Federal law enforcement officials say their agencies frequently must store weapons _ everything from handguns and ammunition to semiautomatic rifles and flash grenades _ inside buildings frequented by civilians, but that those who handle them are carefully trained and abide by existing laws.

The Customs Service acknowledged it possessed the TOW missile in the Murrah building. When its discovery in the rubble sparked alarm, a Customs agent attempted to assure rescuers the missile was unarmed and pleaded unsuccessfully not to delay the rescue efforts.

``The Customs agent offered to personally remove the inert TOW missile from the building,'' the service said in a statement to AP. ``Rescue officials did not take up the agent's offer.''

Customs said the missile was marked live because it ``must appear to be live in order to gain the confidence of suspected arms traffickers during undercover investigations.'' But the agency added it believes its storage in a ``reinforced strong room'' was legal.

``Customs' actions in possessing and storing this system were completely within the law,'' the agency said. It would not discuss the details of the planned sting.

The FBI eventually took custody of the missile and traced the weapon's history from its creation and initial firing at an Alabama Army depot to its reconfiguration with a dummy warhead.

One military expert told the FBI that even an inert missile could pose dangers. ``He stated that inert TOW missiles are still operational. ... These missiles are still fireable as they contain an engine which is propelled by rocket fuel,'' an FBI report said.