China's announcement that its grain crop has "reached last year's levels" actually means that production has dropped, severely affecting the eating habits of millions of Chinese peasants, and adding to Peking's political troubles, agricultural experts here say.

Analysts who have been carefully checking Peking's consistently upbeat crop reports against actual trade figures said yesterday's official claim fits a well-established pattern of using vague claims of no change to mask actual wheat and rice failures. Some observers estimate that the Chinese grain harvest, hard hit by drought and cold, may actually have dropped five million tons from last year's already disappointing 285 million tons, forcing the Chinese to buy more grain abroad and fill their stomachs with tons of sweet potatoes they have been planting in anticipation of a bad year.

"They don't like them," said one analyst of the Chinese attitude toward the sweetish, edible roots, "but it's better than going hungry."

The lengthy New China News Agency report late yesterday of how drought, cold and storms have ravaged China's farm crop indicates a ticklish political problem for the administration of Chairman Hua Kuo-feng.

Still shaky after a year of infighting and political purges following the death of Chairman Mao Tse-tung, Hua's government needs widespread support from the traditional power base of the Chinese Communist Party, the nation's 700 million peasants, so that it can effectively attack the grain problem. But the revelation of farm shortages indicates the peasants may have more to complain about now than they had even during the last few tumultuous years under Mao.

Perhaps the most disheartening item in yesterday's report for both city and country dwellers in China was a signal that earlier reports of increased vegetable oil production were wrong. In October the government's chief economic planner, Vice Premier Yu Chiu-Li, said "Oil bearing crops" had enjoyed a better harvest this year, but yesterday's report dropped them from the list of crops with increased output. Cotton, tobacco and tea were on the list.

The strict rationing of vegetable oil is particularly annoying to husbands or wives preparing Chinese meals. A wallposter in Shanghai earlier this year pleaded with authorities to ease the restrictions. The new report suggests this will not happen, and invites speculation that government planners who have been complaining of overblown agricultural reports from some localities found the earlier figures on oil bearing crops particularly exaggerated.

Hua and the new adminstration's key policy-maker, Vice Chairman Teng Hsiao-ping, have betrayed some concern over the political impact of the crop figures in the last few days. The official press has been full of promises to mechanize farming inorder to improve harvests. On Dec. 25 the People's Daily printed front page pictures of Hua, Teng and other top leaders inspecting new farm equipment. On Dec. 26, the anniversary of the birth of Mao, the newspaper prominently displayed two hitherto unpublished statements by the late party chairman favoring rapid farm mechanization.

Peking has already contracted this year for imports of more than seven million metric tons of grain, a sure sign that "their reserves have neared rock bottom," one analyst said. Most of this grain has been brought from Canada, Australia and Argentina, with rumors but no confirmed reports of some additional purchases from U.S. grain dealers.

Sources here close to commodity markets say they have more solid information that U.S. traders did recently sell the Chinese a large quantity of vegetable oil, perhaps as much as 60,000 tons which would be worth more than $20 million. The Chinese are reported to have bought an additional 20,000 tons of cooking oil elsewhere.

Peking's reluctance to resume heavy purchases of U.S. grain like those in 1973 and 1974 might stem from the current deadlock in U.S.-Chinese diplomatic relations, but traders here think American resistance to certain Chinese grain trade demands has more to do with it. The Chinese insist on the right to base final payment on the quality of the grain after it has reached Chinese ports. Unlike government-backed grain traders in Australia and Canada, American traders are unwilling to take the risk of damage to the grain after it has left U.S. ports and can no longer be supervised by them.

Peking tried to buy a substantial quantity of U.S. grain recently when Canadian and Australian stocks ran out, but negotiations bogged down over the issue of where it would be inspected. About five million tons of non-U.S. grain already contracted for will be delivered to China in the first six months of 1978. After that the Canadians and Australians will have new crops to sell to Peking, so experts here think the chances of future U.S. grain sales to China are poor.

The Chinese crop report said, "This year was one of the worst in the 28 years since liberation, in terms of magnitude of natural disasters and total affected hectarage," a statement with which most foreign analysts agree.

"The spring drought was on a scale rarely seen in the past two decades," the report said. "Exceptional cold hit some parts of northern China and areas south of the Yangtze in January and February. In addition mountain torrents, waterlogging, wind and hail storms insect pests and plant diseases occurred in some areas, and Kiangsu, Shanghai and Cheiaing were hit twice by typhoons."

For once, the infamous "Gang of Four," the dogmatic Peking faction purged by Hua and the army shortly after Mao's death last year, escaped the blame they have been regularly receiving for China's troubles. The report mentioned the gang only once, and then only in a section describing how several provinces badly affected by the gang in 1976 had made progress in restoring production.

The report did not mention many of the North China provinces where crop failure is known to have been most severe. It dwelt on the success of some provinces, like Szechwan in the southwest and Heilungkiang the northeast, in bouncing back from bad years in 1976.

Though mechanization and increased use of chemical fertilizer, China can substantially improve harvests in the near future, Chinese and foreign experts say. To some extent, however, improvements require the purchase of foreign technology and equipment.With its population still growing by at least 16 million persons a year, equalling the previous year's harvest only means still less to go around.