Lashed by unseasonable rain and hailstorms in the rich agricultural belt in the Punjab and other northern states and parched by severe drought in the southern states, Indian crops this season are facing significant damage for the second successive year.

While it is still too early to assess the extent of the damage, agricultural experts say that erratic weather conditions are certain to exacerbate cumulative food grain shortfalls resulting from similar untimely rainfall last spring and the late arrival of the rain-bearing monsoon winds in the summer.

Last year, agricultural production in India is reported to have fallen by 7 percent--compared to a 6 percent increase in the 1981-82 fiscal year--resulting in no increase in the gross national product growth rate, a dramatic drop from the previous 6 percent. Agriculture accounts for 48 percent of India's GNP.

Five years after attaining virtual self-sufficiency in food, India is faced for the second year in a row with the prospect of having to import wheat to replenish reserve stocks if crop damage continues this spring. Last year, India imported nearly 4 million tons of wheat--valued at $654 million--from the United States.

While trying to be as optimistic as possible on the situation, Indian agricultural officials say the overall wheat harvest would still be good if there are no further rains in the north before harvest, and that additional imports are not being considered at the moment.

However, the appearance of the vast wheat fields in this fertile region of the Punjab--traditionally the "breadbasket" of India--suggests otherwise.

Ripe or nearly ripe wheat in many rain-soaked fields is lying flat on the ground, a condition that farmers called "lodged" and which, in effect, is the same as if the wheat were cut and left to spoil in the rain. The excessive moisture can cause a fungus called karnal bunt, which ruins the wheat or sharply reduces its quality and selling price.

State agricultural officials in normally drought-prone Rajasthan have issued preliminary estimates of 20 percent to 30 percent crop loss due to rain, and officials in Uttar Pradesh said a large amount of harvested wheat in that state had been ruined.

Last April and May, unseasonable rainfall in the Punjab and the neighboring states of Haryana and Uttar Pradesh destroyed an estimated 2 million tons of wheat in the fields, but, more important, caused extensive quality deterioration in much vaster amounts of wheat. The extent of damaged wheat has not yet been pinpointed. The combination of the erratic monsoons of last summer and the unexpected rains last spring reduced foodgrain production nationwide to 124 metric tons, down from a record 133 million in the 1981-82 fiscal year. Last year had been declared the "Year of Productivity" by the Indian government.

Before this month's uncommonly late rainfall, U.S. Embassy agricultural experts in New Delhi who closely monitor Indian food production had predicted in a report issued in February that because of favorable weather during the growing season, food grain production in the spring harvest would reach a record 55.5 million tons nationally, including 38.5 million tons of wheat.

Now, the experts say, the spring harvest has become a "guessing game," and the outcome will depend on how much harvested wheat has already been destroyed on the ground, and how much uncut wheat will be found to have been damaged.

"It probably won't be quantity loss as much as quality loss," one U.S. agricultural official said, adding that last year the Indian government was forced to purchase large amounts of moisture-laden wheat at reduced prices.

Paradoxically, southern India has sustained extensive rice crop losses because of one of the most severe droughts in recent times.

State agriculture officials in Tamil Nadu, which normally grows nearly 6 million tons of rice a year, have said this year's total harvest, including the monsoon crop, will be only 2.8 million tons, although other analysts say the yield will be closer to 4 million tons.

Similarly, Orissa, which usually produces 4.2 million tons of rice annually, will yield 40 percent less this year, local officials predict.