FEDERAL ethics watchdogs are on a collision course with federal scientists. Proposed conflict-of-interest rules would restrict participation of United States executive-branch employees in the affairs of their nonprofit professional societies. For scientists, this would seriously weaken their professional standing.This is a needless controversy - more a clash of two quite different cultures than a substantive issue. The scientific culture traditionally features openness, sharing, and collegiality. The watchdog culture features suspicion and rulemaking. Each culture has its strengths and weaknesses. Certainly the easygoing scientific culture has sometimes led to ethical laxity, including improper liaisons between federal employees and outside interests. And agency watchdogs have been properly faulted for not being more alert to scientists' misconduct. But that failing shouldn't be addressed by undermining a strength of the scientific culture: the contribution of individual scientists - regardless of employment - to the national and global scientific com munity. Scientists make much of their contribution to scientific society through professional associations, plus such overarching entities as the National Academy of Sciences and various international scientific unions. These groups set professional standards, publish much of the scientific literature, and hold meetings where research is reported and discussed. Federal government scientists have traditionally been encouraged to participate fully in these organizations. But under rules proposed by the Office of Government Ethics, federal employees would generally be prohibited from such participation on government time. It would be virtually impossible to maintain such participation in off-duty time. The new rules thus would effectively exclude a large part of the American scientific community from essential professional activity. Existing laws and ethical regulations should cover any conflict-of-interest problems professional association work might involve. The new rule would only further discourage talented scientists from accepting government employment.