ASHINGTON, Oct. 23 — In the what's-next guessing game that began after the terrorist attacks last year, a divide has opened up among experts assessing the risk to the public from attacks on nuclear power plants.

Many current and former government officials say the reactors are in Al Qaeda's cross hairs, but inside the industry, many executives counter that what drives the issue is politics and unreasoning fear.

Current and former high-ranking officials at Andrews Air Force Base in Maryland for a recent exercise on how to cope with terrorism illustrated this divide. Over two days, they simulated a meeting of the National Security Council and were fed hypothetical situations in which intelligence, vague and conflicting at first but becoming more specific as the hours went by, indicated an attack somewhere in the eastern United States.

They were also given an assessment that said that the targets vulnerable to the widest range of threats were not nuclear reactors, but places where chemicals were manufactured or stored.

Almost immediately, the role-players shifted the discussion to how to protect the reactors.

"The players defaulted in that direction," said Dave McIntyre, the deputy director of the Anser Institute for Homeland Security, a nonprofit group that sponsored the exercise with the Center for Strategic and International Studies.

Mr. McIntyre said he thought the concern with reactors was an unnecessary detour, because their security had been improved far more than security for other potential targets. But the group did not see it that way.

Reporters who were allowed to sit in on the exercise had to agree not to quote the participants, to allow them, the sponsors said, "to be as open and candid as possible" in the drill.

The group included former Senator Sam Nunn, playing the president; James M. Loy, the head of the Transportation Security Administration, playing the role of secretary of homeland security; Charles Curtis, a former under secretary of energy, playing energy secretary; George Terwilliger, former acting attorney general, as attorney general; R. James Woolsey, the former C.I.A. director, as national security adviser; Wesley Clark, the former supreme allied commander in Europe, as chairman of the Joint Chiefs of Staff.

Other participants played the jobs they used to have: James S. Gilmore III, former governor of Virginia; Shirley Jackson, former chairwoman of the Nuclear Regulatory Commission; James Lee Witt, former head of the Federal Emergency Management Agency, and Dee Dee Myers, a former White House spokeswoman.

They explored creating a 50-mile zone around each nuclear plant where all flights would be banned, or bringing in antiaircraft batteries.

On the other side, some people outside the simulation who are actually in charge of security at nuclear plants say they do not believe that they are threatened by terrorism, and are unenthusiastic about security improvements.

Mark P. Findlay, the director of security at the Nuclear Management Company, which operates six Midwestern reactors, said in a telephone interview that there had been no credible threats against nuclear plants, and that he would prefer not to hire more guards now, for fear of having to lay them off later.

"How do I deal with staffing levels when I have a government that's based on politics and not events and credible threats?" Mr. Findlay said.

The airlines might once have said the same, and there have been attacks on nuclear plants abroad.

Mr. Findlay is not alone. Last month, 19 current and former executives in the nuclear power plant field published a paper in Science magazine that asserted that a reactor could easily withstand a crash of the kind that destroyed the World Trade Center, a position disputed by others, including some on whose work the authors relied. The Science article argued that talk of vulnerability was simply wild-eyed conjecture by people who never liked nuclear power anyway.

That category includes at least some local government officials who are now uneasy about the reactors in their midst. In the neighborhood of the Indian Point reactors, 40 miles north of midtown Manhattan, local governments have passed resolutions against them. In Westchester County, where the two plants are, the County Board of Legislators voted on Sept. 9 to close them eventually.

If the plants are so safe, why are so many people worried about them?

"The news media has made the nuclear industry the poster child for the post-Sept. 11 world," said Steve Kerekes, a spokesman for the Nuclear Energy Institute, the industry's trade association. "People who have been inundated for a year now gravitate toward that topic."

"Some media grad student ought to do a study of air time and column inches dedicated to the subject," Mr. Kerekes said.

Peter Stockton, a nuclear security expert who is a former special assistant to the secretary of energy, drew a different conclusion. Mr. Stockton, who now works on civilian power plant security questions with the Project on Government Oversight, a nonprofit group here, said the power plant managers were in denial as the managers of nuclear weapons plants were when he was at the Energy Department.

"They say, `We've been at this for 50 years and we've never been attacked yet,' " he said. "They believe a credible threat is that a terrorist group has targeted that one plant, and they're coming."

Paul M. Blanch, an engineer who found safety problems a decade ago at the nuclear utility where he worked, and whom the Nuclear Regulatory Commission later said was mistreated by his employer as a result, said the denial was "par for the course for the nuclear industry."

"The industry has been defensive about every threat, whether it's security or accident," Mr. Blanch said.

"If something happens, like happened with airlines, maybe they wouldn't be so defensive," he said, "but it hasn't happened yet. "