Nearly three-quarters of the nation's nuclear power plant operators are behind schedule on new federally mandated security upgrades, mostly dealing with truck bombs, according to the Nuclear Regulatory Commission.

Truck bombs are one of the most commonly used and easiest to obtain terrorist weapons, and anxiety about them has grown since Sept. 11. That worry appears to be behind many security upgrades ordered in February by the commission, which governs nuclear plants.

The orders included preparing a detailed analysis on the vulnerability and consequences of a truck bomb attack, commission spokesman Victor Dricks said Thursday.

The power plants do not publicly disclose why they need more time, but Dricks said nearly 90 percent that say they can't make their deadlines are having problems with the truck bomb analysis.

Dricks confirmed that operators at 47 of the 64 clusters of nuclear power plant sites asked for a deadline extension on the new orders. There are 103 operating power plants clustered in 64 sites nationwide.

The need for extensions doesn't mean a truck bomb threat is imminent, and generally plants are ahead of schedule on upgrades. They include more security guard patrols, additional security posts, additional security barriers, vehicle inspection points further from the cores of the power plants and improved coordination with government law enforcement.

In a closed hearing Thursday, a House subcommittee asked Nuclear Regulatory Commission officials about security and truck bomb planning. While industry plans are delayed, "I'm not upset that there's any lack of commitment," subcommittee chairman James Greenwood, R-Penn., told Knight Ridder afterwards. "It's just a question of a very technical matter to provide the NRC with the information it needs."

"I think Americans can feel pretty darn secure that their nuclear power plants are not going to be compromised by terrorists," Greenwood said.

Nonetheless, plants that aren't secure against truck bombs aren't as safe as operators have been saying, claimed Edward Lyman, the scientific director of the anti-nuclear organization Nuclear Control Institute of Washington.

"They can't assert they are fully protected about whatever new threat is out there if they haven't even done the analysis to assert that they are protected from vehicle bombs," Lyman said. "If they're delaying providing a schedule for two or three months ... then how are they going to get contracts in place to do work to build vehicle barriers or additional protection?"

But Ann Mary Carley, a spokeswoman for Exelon Generation of Warrenville, Ill., which operates 17 nuclear power plants, said her company needed a delay so "that when we evaluate what needs to be done, we're doing what is actually going to protect us."

Even if a truck bomb went off, it is unlikely to cause the runaway type of nuclear catastrophe that many people fear, said Harold Denton, a retired reactor regulation chief for the Nuclear Regulatory Commission. He oversaw the commission's response to the Three Mile Island nuclear plant accident in March 1979 and was the first American official to visit the site of the April 1986 Chernobyl nuclear disaster.

A truck bomb attack might be bad, "but it doesn't lead to Chernobyl," Denton said.

The greatest worry is that the explosion would knock out power required to run pumps that bring in water to cool the nuclear material, Denton said. If the power went out, control rods would stop the nuclear reaction within a matter of seconds, but it could take weeks of electric power and water pumping to cool all the nuclear material to safe levels, he said.

Still, almost every power plant has enough backup power batteries, generators, steam turbines to provide at least eight hours of cooling before additional help could come, Denton said.

Since the Sept. 11 terrorist attacks, U.S. intelligence and law enforcement officials have identified several potential threats to nuclear power plants.

The Nuclear Regulatory Commission asked for 1,950 "interim corrective measures" at the nation's nuclear power plants last February with a variety of deadlines that all led up to a final deadline of Aug. 31.

Plant operators requested a deadline extension for about 65 specific measures, Dricks said. He predicted that all but three or four nuclear power plant operators would meet the deadline.

Steve Kerekes, spokesman for the Nuclear Energy Institute, a Washington, D.C., organization consisting of nuclear power plant operators and suppliers, said most of the security measures are already in place.

"We were well defended on Sept. 10 and we are even better defended today," Kerekes said.

The following clusters of power plants have asked for deadline extensions for security upgrades:

Beaver Valley of McCandless, Penn.; Calvert Cliffs of Calvert Cliffs, Md.; James A. Fitzpatrick of Oswego, N.Y.; Limerick, west of Philadelphia; Milestone of New London, Conn.; Nine Mile Point of Oswego, N.Y.; Oyster Creek of Toms River, N.J.; Peach Bottom of Lancaster, Penn.; Ginna of Rochester, N.Y.; Seabrook, south of Portsmouth, N.H.; Susquehanna of Berwick, Pa.; Three Mile Island of Harrisburg, Pa.; and Vermont Yankee of Battleboro, Vt.

Browns Ferry of Decatur, Ala.; Catawba of Rock Hill, S.C.; Edwin Hatch of Baxley, Ga.; Joseph M. Farley of Dothan, Ala.; McGuire, south of Charlotte, N.C.; North Anna of Richmond, Va.; Oconee of Greenville, S.C.; Sequoyah of Chattanooga, Tenn.; St. Lucie of Fort Pierce, Fla.; Turkey Point of Miami; Summer, northwest of Columbia, S.C.; Vogtle, southest of Augusta, Ga.; and Watts Bar of Spring City, Tenn.

Byron of Rockford, Ill; Clinton of Clinton, Ill.; Davis-Besse, southeast of Toledo, Ohio; Donald C. Cook of Benton Harbor, Mich.; Dresden of Morris, Ill.; LaSalle of Ottawa, Ill.; Perry of Painesville, Ohio; and Quad Cities, northeast of Moline, Ill.

Arkansas of Russellville, Ark; Callaway of Fulton, Mo.; Comanche Peak of Glen Rose, Texas; Diablo Canyon, west of San Luis Obispo, Calif.; Fort Calhoun of Omaha, Neb.; Grand Gulf of Vicksburg, Miss.; Palo Verde, west of Phoenix; River Bend, north of Baton Rouge, La.; San Onofre of San Clemente, Calif.; South Texas Project, south of Bay City, Texas; Waterford, west of New Orleans, and Wolf Creek of Burlington, Kan.

The following clusters of power plants did not ask for deadline extensions for security upgrades: Hope Creek of Wilmington, Del.; Indian Point, north of New York City; Pilgrim of Plymouth, Mass.; Salem of Wilmington, Del.; Brunswick of Southport, N.C.; Crystal River of Crystal River, Fla.; H.B. Robinson of Vicksburg, Miss.; Shearon Harris of Raleigh, N.C.; Fermi, north of Toledo, Ohio; Columbia of Richland, Wis.; and Cooper of Nebraska City, Neb.

The following cluster of power plants weren't quite clear about a deadline extension in their public letters but don't seem to be asking for an extension: Duane Arnold of Cedar Rapids, Iowa; Kewaunee, east of Green Bay, Wis.; Monticello, northwest of Minneapolis; Palisades of South Haven, Mich.; Point Beach of Manitowoc, Wis.; and Prairie Island, southeast of Minneapolis.

2002, Knight Ridder/Tribune Information Services.