IT'S RIGHT for the United States to extend a hand to the struggling Mikhail Gorbachev, as President Bush has just done in offering to let Moscow buy $1 billion in agricultural products on official credit. The step is a low-cost investment in the political survival of a Kremlin worthy and in the goodwill of the Soviet people. Soviet food distribution is a mess, and there are spot shortages and pockets of distress.

One needn't get too effusive about the humanitarian aspect of it all. Helping others buy American farm exports is normal commercial practice in today's soft world grain market -- "aid" but less to the buyers than to the sellers. American farmers were clamoring for relief from low wheat prices and the narrowed supports in the new farm bill. They will profit from the new credits, and some Soviet citizens will eat better.

But which? The food will come with advice in food distribution. But Soviet food distress flows much less from technical problems than from the struggle to build a new society and from the decisions people take -- withholding supplies, hoarding, bartering, stealing, black marketeering -- to endure or exploit the transition. The Bush administration hopes that the new American sales and the much larger food sales from other countries will restore consumer confidence and calm the market. Good luck.

Meanwhile, American food will be bolstering the central government, its purchaser and distributor, rather than recipients at the republic or local level, in at least two specific ways. One is to enforce discipline: the prevailing chaos has led Mr. Gorbachev to assign the KGB to police food distribution. The other is to give him a potentially useful tool in his political battle to revise relations between the union and the republics.

To offer the new credits, President Bush had to waive (for six months) the famous 1974 Jackson-Vanik amendment, which hinges Soviet trade with this country on free emigration from the Soviet Union. He did so because, although Moscow has not met his condition of writing its new emigration policy into law, Jews -- politically, the key group -- are now leaving faster than they can be resettled abroad.

Actually, he didn't waive Jackson-Vanik but only the farm-credits corner of it. He ought to waive the whole thing. Soviet liberality on emigration thoroughly justifies it. The law inscribes high punitive tariffs whose lowering to normal levels could be of value to the United States and to the Soviet Union or any emerging successor states.