WASHINGTON  — FEMA will replace locks on as many as 118,000 trailers used by Gulf Coast hurricane victims after discovering the same key could open many of the mobile homes.

One manufacturer cut only 50 different kinds of keys for the trailers it sold to FEMA, officials said Monday. That means, in a worst-case scenario, one key could be used to unlock up to 10 mobile homes in a park of 500 trailers.

FEMA officials said such a situation was unlikely, but they still moved to warn storm evacuees living in Louisiana and Mississippi trailer parks of the security risk.

“We are working aggressively to establish the extent of the problem and determine the best solution for the safety and security of those who now reside in these trailer units,” said Gil Jamieson, deputy director of Gulf Coast recovery for the Federal Emergency Management Agency.

He said FEMA was “asking residents to be extra vigilant and take precautions to secure the trailer that they occupy.”

“We encourage them to work together to promote a neighborhood watch and help ensure the safety of all residents,” Jamieson said.

Dane St. Pe, who lives at a FEMA trailer group site in Bay St. Louis, Miss., said he had heard that you could use common keys to open more than one trailer.

“One of the kids was saying that, and I didn’t believe him,” said St. Pe, 37, an electrical contractor.

A nine-year-old girl in the same encampment said her friends had used the key from their trailer to open a storage compartment on her family’s trailer, but that it didn’t work on the trailer's door.

It is unknown how many trailers will need to have their locks replaced, said FEMA spokesman Pat Philbin.

Sen. Mary Landrieu, D-La., called the lock risk “very troubling.”

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“While this development certainly adds to a long list of oversights lost in the dysfunctional bureaucracy of the agency, I’m encouraged that FEMA has already begun to take steps to ensure the security of the residents entrusted to it,” Landrieu said.

FEMA provided about 77,000 trailers for Hurricane Katrina evacuees in Louisiana, said state emergency management spokesman Mark C. Smith. He said the largest trailer park for hurricane evacuees in the state was Renaissance Village, just north of Baton Rouge, La., with an estimated 480 mobile homes.

Only three kinds of locks
The problem stems from a limited number of kinds of locks — three — that trailer manufacturers use when building mobile homes, FEMA officials said. That increases the likelihood of locks being the same, they said.

One manufacturer cut only 50 different patterns for the first set of locks used in the trailers, Philbin said. Another manufacturer cut 100 and 200 patterns for the second and third kinds, he said.

Philbin did not immediately know how many trailers were distributed for each key cut. In all, the agency has issued about 150,000 travel trailers and mobile homes to evacuees since Hurricanes Katrina and Rita slammed into the Gulf Coast last year. About 32,000 have been taken out of service, Philbin said.

In the meantime, FEMA has asked local police to increase patrols in the trailer parks and is distributing flyers to residents. FEMA security personnel and contractors also are on guard for suspicious behavior, Philbin said.

Residents who want new locks can request them from the trailer park’s manager or service provider, FEMA officials said.

The Associated Press and MSNBC.com's Mike Brunker contributed to this report.