Nuclear walkout

The United States has given welcome assurances that it will uphold international nuclear safeguards even while it pursues the extraordinary step of considering withdrawal from the agency charged with maintaining them. Now care must be taken to avoid undermining these safeguards through doubts about genuine US commitment to preventing nuclear weapons proliferation. These have been raised by the US walkout from last month's International Atomic Energy Agency conference in Vienna - and the current reassessment of vital American participation in and financial support for what Washington acknowledges is the IAEA's ''critical'' safeguard role.

The US walkout was joined by 15 other nations. It was in reaction to the conference's rejection of the credentials of Israel, whose 1981 raid on an Iraqi reactor and supposed development of nuclear weapons came under attack.

Washington declared that here was an example of the politicization that damages international agencies - and that it was determined to prevent the spread of it. What it needs to do now is dispel the notion that it was simply letting US support of Israel override the larger issue of nuclear nonproliferation.

The United States has frequently and quite properly opposed the exclusion of South Africa as well as Israel from United Nations forums. The reasoning is sound that even violators of UN mandates can be dealt with more effectively through inclusion than ejection.

By the same token, nations that uphold UN mandates can be more effective through vigorous participation than through protests from the sidelines. In the case of the International Atomic Energy Agency, the US has made its point against politicization in one way by walking out of a conference. It can make it more credibly by wholeheartedly returning to support of the agency in its nonpolitical aspects. Washington risks the appearance of its own brand of politicization by leaving its commitment in the limbo of ''reassessment.''