Scientists at the nation's nuclear weapons laboratories must report any romantic liaison with a foreigner, unless it's a one-night stand.

That, in a nutshell, is the new policy announced by the Department of Energy (DOE) as part of a wide effort to tighten security at the labs in the wake of a Chinese espionage scandal, an effort that members of Congress say is long overdue but that is causing confusion, anxiety and derision in the scientific community.

The security crackdown also includes: a proposal to require an estimated 5,000 nuclear scientists to undergo polygraph examinations; an array of cybersecurity measures tightly regulating data transfers and e-mail; and provisions requiring extensive background checks on foreign visitors to the weapons facilities.

Opposition is growing among scientists to the polygraph provision, and DOE officials in Washington worry that the stringent background checks on foreign visitors could prompt some countries to retaliate, harming U.S. initiatives to safeguard nuclear material in the former Soviet Union.

The most derided new policy, however, requires DOE employees who hold security clearances to report any "close and continuing contacts" with foreigners from 25 so-called sensitive countries, a list that includes China, Russia, India, Israel and Pakistan.

The policy went into effect in July and was slightly modified and reissued in mid-August by Edward J. Curran, the department's director of counterintelligence, after some employees asked for a definition of "close and continuing."

The new definition, reported yesterday by the Albuquerque Journal, exempts one-time sexual relationships from the reporting requirement if there is no expectation of future contact, no indication that a lab employee has been targeted for espionage, and no request by a foreigner for classified or sensitive information.

"You can take it and ridicule it," Curran said in an interview. "But we had to define contacts because the scientists said they couldn't do it for themselves."

Curran lamented that "common sense doesn't prevail" at the labs, and he said that in the past, there has been almost no control "over who was talking to whom."

"You know [counterintelligence] is working when you get resistance to it," he added.

One senior manager at Los Alamos National Laboratory, who asked not to be quoted by name, maintained that scientists have long reported suspicious contacts. "There's always been the requirement that you have to report any significant ongoing or unusual contact with a foreign national; that's been in existence for years," the official said. "My experience is that people have always been pretty good about reporting incidents that raised red flags with them."

Similar reporting policies are in place at the FBI, CIA, National Security Agency, Defense Intelligence Agency and Department of Defense. Diplomats stationed in some countries also are required to report on their relationships with foreigners.

Curran, a career FBI official who is considered the federal government's leading counterintelligence investigator, went to the DOE following a February 1998 presidential directive to beef up security at the nation's nuclear weapons facilities.

President Clinton issued the order partly in response to the espionage investigation at Los Alamos where Wen Ho Lee, a Chinese American physicist, was fired in March for security violations and was identified as the government's prime espionage suspect.

Lee has denied passing secrets to China, and U.S. officials now concede that they lack evidence to charge him with espionage. The U.S. attorney in Albuquerque is still considering whether to prosecute him for transferring nuclear weapons data from the lab's classified computer network to his unclassified desktop computer.

Since firing Lee, Energy Secretary Bill Richardson has taken a series of steps, in concert with Curran, to heighten scientists' awareness that they may be targets of foreign intelligence operatives.

Richardson temporarily shut down all computing systems at the labs for a security review and has twice ordered day-long security "stand downs" at Los Alamos and Sandia National Laboratories in New Mexico, and Lawrence Livermore National Laboratory in California.

Hearings on the polygraph proposal are scheduled for later this month at all three labs, where some scientists question the validity of polygraph testing and say such tests may ruin the careers of innocent employees as well as reduce the labs' ability to attract top scientists.

The new policy on "close and continuing contacts" says that any sexual or intimate relationship, sharing of living quarters, or business or financial relationship with a foreigner from a sensitive country must be reported to counterintelligence officials within five days.

Social contacts and nonsexual personal relationships also must be reported if "sensitive professional and personal information is discussed or is the focus of discussion."

One-time sexual relationships don't have to be reported. But if an employee has had sex with a foreigner "on more than one occasion" the relationship must be disclosed: "Such contact must be reported regardless of whether the foreign national's full name and other biographic data are known or unknown."

The policy notes that conversations on the Internet can be considered "close and continuing contacts" because foreign intelligence services often use cyberspace "as a valid way to conduct business."