THE food problem in Russia and the other former Soviet republics won't be solved by rush shipments of Western grain to get people through the winter. That help is needed and should be forthcoming, especially in light of this year's poor harvest. But the problem lies deeper than the impending shortage.Some Western experts say the critical difficulty is distribution, not production of food. Certainly decrepit transportation and storage systems must be modernized. Equally important, however, is communism's continued grip on the prime agricultural asset - land. Local party chiefs may mouth reform, but they hold fast to the old dogmas. This state of affairs was dramatically conveyed to Americans last week by a segment on the McNeil-Lehrer NewsHour. It examined the frustrations faced by Vladimir Plotnikov, a Russian private farmer who leases 15 acres just outside of Moscow. He leases because he still can't legally own, and his landlord is a nearby collective farm. Mr. Plotnikov and his handful of workers far out-produce the collective. To squelch the upstart, party operatives manipulate a meeting of the district council. Plotnikov's request to lease more land is turned down, and he may not even be allowed to renew his present lease. One party official acknowledges that in this age of reform his district doesn't yet have a single private farmer who owns his land. "It's very difficult and complicated and takes time," he says. And he intends to keep it just as difficult as possible. Plotnikov, whose father was a kulak, a private farmer driven from the land by Stalin, isn't giving up. "I want to bring state-of-the-art private farming to the Moscow area, and I will continue whatever happens." We hope Russia's reformers hear him and make private property an economic fact of life. Farmers like Plotnikov are essential to a permanent solution to the food problem.