Savannah River Site temporarily stopped operations at its nuclear-processing facilities, said Rick Ford, an SRS spokesman.

Most of the federal nuclear-weapons site's day-shift employees were sent home just before 1 p.m., although a few SRS officials remained behind, in part to man the site's Emergency Operations Center, Mr. Ford said.

The site closed to all visitors and vendors, said Mickie Seitter, a spokeswoman for SRS contractor Westinghouse Savannah River Co. Employees leaving SRS were told they could not return that day.

But second- and third-shift employees reported to work as usual, said Julie Petersen, an SRS spokeswoman. Day-shift workers were told to report at their regular times today, Ms. Petersen said.

Security guards at SRS, armed with automatic weapons, direct traffic leaving the site after a majority of the daytime work force was sent home just before 1 p.m. in the wake of apparent terrorist attacks. RON COCKERILLE/STAFF

The shutdown affected not only SRS, but also nuclear-weapons sites across the country, Mr. Ford said.

''As a prudent measure and per our security procedures, we are suspending nuclear materials processing activities,'' he said.

Wackenhut Services Inc., the private security company that serves as the site's police force, increased security along site roads and stepped up inspections at SRS barricades, said Wackenhut spokesman Rob Davis.

Beyond that, site officials revealed little.

''We've taken some extra precautionary measures that we can't get into for security reasons,'' Mr. Davis said.

The site long has prepared for attacks out of concern that terrorists might try to steal the materials needed for an atomic weapon. The site treats and stores plutonium, and also recycles tritium, the radioactive, gaseous form of hydrogen used in modern nuclear weapons.

Fort Gordon also increased security measures after the attack, as did military bases across the country. Visitors were not being allowed onto the Army base, said Marla Jones, a fort spokeswoman.

Plant Vogtle also heightened security after the attacks, said Rick Kimble, a spokesman for Southern Nuclear Operating Co. in Birmingham, Ala.

Southern Nuclear operates the nuclear-power plant near Waynesboro for Georgia Power Co.

Reach Brandon Haddock at (706) 823-3409 or bhaddock@augustachronicle.com.