China is buying more wheat abroad than in any year since 1974, butressing indications that the supply of food in the country this winter is much tighter than usual.

Including a deal for 2 million metric tons from Australia announced yesterday, Peking has contracted to buy 5 million tons abroad this year at an estimated cost of $550 million.

In recent months, markets here have seemed to have less and poorer quality food and there have been unconfirmed reports in cutbacks in rice rations in some areas of southern China.

Foreign analysts here are beginning to question official claims that last year's grain harvest equalled or suprassed that for 1975. They suspect it was only marginally better, perhaps by a percentage point or two. This would barely keep up with population increases.

Another factor forcing greater wheat imports is undoubtedly the deterioration in China's railroad system. The current leaders blame it on labor unrest fomented by the radical "Gang of Four".

The need to spend more on wheat imports comes at a time when China is already spending more money for increased imports of steel made necessary by labor unrest and a continuing coal shortage. In conversations with foreigners, Chinese officials have said that steel production fell 20 or 25 per cent last year.

(A Department of Agriculture specialist on China said analysts in Washington have proposed several other theories for China's need to buy more railroads and an inadequate harvest in 1976. He said these include continuing problems stemming from last year's massive earthquake in Hopeh Province and political unrest in the countryside. In the latter case, however, the specialist said, there has been more specific supporting evidence.)