After four years of self-sufficiency in food grains, India has been forced into the international market to buy 1.5 million tons of wheat from the United States to fill its dwindling reserve stocks.

Prime Minister Indira Gandhi said her government is buying the wheat as an antiinflationary measure to fight the market machinations of traders and hoarders.

"I believe in stocking up," when things are inexpensive and readily available, she explained. "We don't find it necessary," she said later, "but we find it expedient."

The purchases aroused a storm of protest in newspaper editorials and from politicians, especialy since India has boasted often of its newly won ability to feed its 684 million people with home-grown grain. Moreover, India was able to get through the 1979 drought, on of the worst in the century, without a famine or having to purchase grain from abroad.

The Indian Express called the wheat purchase "more shocking results of the government's economic mismanagement."

"India's self-sufficiency in food grains has been its most shining achievement in the eyes of the world. The incongruity of our resorting to imports cannot escape international attention."

Even politicians of Gandhi's Congress-I (for Indira) Party complained the money should have been spent on the Indian farmers.

Opposition leader A. B. Vajpayee, the former foreign minister, called the decision to buy American wheat "a national disgrace" and "a betrayal of the Indian farmer."

"The spineless Congress-I government is our with a begging bowl in the United States," he said, demanding a national boycott of the wheat.

Nonetheless, it is clear here that the Gandhi government got a good deal for the U.S. wheat. The purchases, at about an average price of $172 a ton, were made at a time when wheat prices in America are depressed and before expected Soviet and Chinese purchases.

The totla purchase price has been reported here at about $260 million.

The purchase comes amid estimates of a record Indian wheat crop of about 36 million tons. Outside observers, however, believe these reports are unduly optimistic. U.S. satellite photos, for instance, indicate a crop of about 33.7 million tons.

Moreover, there are reports that big farmers and traders are hoarding wheat and refusing to sell it to the government for reserve stocks and cut-rate fair-price shops.

The government purchase price of $162.50 a ton, about the same as it will pay the United States, is below the current market price of $187.50 to $200 a ton. In some states, sources said, the price is as high as $250.

But Westerners traveling through India recently report no signs of hoarding and say the high market price indicates real shortages.

The dwindling government grain stocks came after a monsoon in 1979 that forced India to dip into its reserve stocks to feed the country.

This was done, however, without having to purchase wheat abroad, which led Indian officials and such international organizations as the World Bank to proclaim that Indian agriculture had at last escaped from the vagaries of the weather and that the country was now self-sufficient in food grains.

But a weak monsoon last year brought a second lower-than-expected wheat crop and another call of India's reserve stock.

Before the 1979 drought, India had more than 20 million tons of food grains, mostly wheat and rice, in reserve. That has been drawn down, and in May there were only 3 million tons of wheat on hand in government warehouses.