he monsoon rains hit Delhi on July 29, just as the weathermen predicted. They immediately cooled the air after three months of 115-degree heat, but created chaos in India's capital city by flooding key roadways and severely disrupting communications.

It became a parliamentary scandal as 40,000 of Delhi's quarter of a million phones were thrown out of commission by the rainstorms. It was so bad that four of six telex machines reserved for Prime Minister Indira Gandhi's use stopped working.

But, more important, the onset of the rains gave India the hope of a bountiful harvest and economic prosperity for the coming year.

Now, 2 1/2 months later, that hope has not been fulfilled. Although the monsoon started on time and with a rush, agricultural experts report that it died out early and the rains of late August and early September that are vital for a successful harvest in October never came.

The monsoon rains, which generally end in northern India in mid-September, quit a month early this year. Agriculture Minister Rao Birendra Singh acknowledged the government's concern to Parliament last week, and said that extra water is being released for irrigation and power supplies are being increased for farmers so they can use pumps to water their fields.

Western agricultural experts here whose forecasts have been accurate in the past are predicting that India, which ended four years of self-sufficiency in grains when it purchased 1.5 million tons of wheat from the United States in July, is likely to be forced back into the international market as a result of a poor harvest caused by the early end to the monsoon.

One expert predicted India will have to purchase another 2.5 million to 3 million tons of wheat.

It is, however, a hard political decision for India to take as this country took great pride in its newly won ability to feed its 684 million people with home-grown grains. The original purchase drew a storm of protest from newspapers and politicians, including some members of Prime Minister Indira Gandhi's ruling Congress-I Party.

The reality, though, is that India, like most of the countries of Asia and Africa, is subject to the vagaries of nature. Even with a vast increase in irrigation across the country and the use of fertilizer and miracle seeds, a good monsoon is needed for a bumper crop.

Furthermore, despite its boast of being the 10th largest industrial power in the world, its nuclear reactors and its fledging space program, India remains essentially an agricultural society. Almost 80 percent its people live in its more than half a million villages, 200,000 of which have neither a water supply nor electricity.

To them, the seemingly capricious coming and going of the rains is all important for survival.

For India, this year's monsoon has been one of the most capricious of all. A large portion of the northern Indian state of Rajasthan, for example, suffered through its third year of drought in which farmers could not even get enough fodder to feed their cattle. Yet the capital city of Jaipur was hit by the worst flooding in its history when torrential rains fell in that area of the state.

The fall harvest crops in most of the state are reported to be withering since there has been no real rain since the July deluge. The Indian Express newspaper reported that 20 of the state's 26 districts face famine because the crops either were flooded away or dried out because of lack of rain.

The same is true in Uttar Pradesh, India's most populous state, where worsening floods were reported in its eastern districts and drought in the west.

Experts in that state predicted a 30 percent crop loss from the expected yield of 9 million tons. In the district of Bulandshahr alone, according to the Times of India, sugar cane, corn and millet crops are virtually destroyed and wheat fields lay parched. The total loss was estimated at $50 million.

The rice crop in the state was reported to have been almost totally destroyed.

The chief minister of that state, Vishwanath Pratap Singh, is using police radios to get reports of shortages of power and diesel fuel for irrigation pumps.

The rice crop in the Punjab is expected to be 25 percent less than expected. Moreover, a shortage of fodder caused by the drought has reduced the milk yield of buffalo by as much as 40 percent.

According to reports reaching here, other northern Indian states hit by the early end of the monsoon are Bihar and Haryana, where agricultural experts predict a 30 percent loss in rice crops and a 50 percent cut in corn and millet.

The poor harvest comes at a time when India's reserve stocks are drawn down because of the 1979 drought, considered one of this country's worst. It was India's ability to feed itself from its reserve during that drought without having to buy food grains that led many experts to say it had reached self-sufficiency.

Now, however, reserve stocks are down to 13.5 million tons--including 7 million tons of wheat and 6 million tons of rice--compared to a total of 20 million tons of food grains in reserve last year.