Prime Minister Indira Gandhi today accused the United States of introducing a new generation of weapons to the Indian subcontinent by agreeing to sell advanced F16 fighters to Pakistan.

She called the American first-line jets "a generation ahead of anything operating with other air forces of the area" and said their sale to Pakistan will push the subcontinent "willy-nilly" into an arms race.

Gandhi, who is also India's defense minister, said planes in other South Asian air forces have late 1960s or early 1970s technology, while the F16 is an advanced aircraft of late 1970s technology and operational capability. "In the offensive role," she said in a prepared statement read at a press conference, "it can go much farther and can carry bigger bomb loads. The offensive strike capability of even one such aircraft is at least three times that of the Mig21."

The Soviet-built Mig21 is the workhorse of the Indian Air Force, but Gandhi neglected to mention that India is now being supplied with more modern Mig23s and has on order Mig 25s. Indian military experts said New Delhi already has 26 Mig 23s and at least two Mig25s.

Furthermore, India is also getting British-made Jaguars and is negotiating with France for the purchase of Mirage 2000s, which are still in the developmental stage.

In her wide-ranging press conference, which also touched on domestic politics and India's economy, Gandhi appeared to rule out an Indian nuclear weapons program even if Pakistan develops the ability to make an atomic bomb.

The two neighbors, which have fought three wars since they won independence almost 34 years ago, have major nuclear programs that both say are aimed at the peaceful development of atomic power. But Parkistan is widely suspected to have a nuclear weapons program, and India is believed to be able to convert the technology of its 1974 nuclear explosion into weapons technology.

Gandhi's attack on the U.S. sale of F16s to Pakistan comes at a time when U.S.-Indian relations are deteriorating because of the Reagan administration's effort to forge close ties with Islamabad and because of what appears to be the coming cancellation of an American agreement to supply nuclear fuel for an Indian atomic reactor at Tarapur. A high-level U.S. team starts meetings here about Tarapur Monday.

The currrent strains between Washington and New Delhi are so great that the chief American diplomat here, charge d'affaires Archer K. Blood, counseled during his July 4 speech to the American community "patience and understanding of India in the difficult days ahead."

"There's no doubt," he said later, "that United States and India, our host country, and I don't see any hope of improvement soon."

While Gandhi, relaxed and smiling, spoke in soft tones during her 75-minute press conference, she made it clear that her target was as much the United States as Pakistan.

"We are against the collection of highly sophisticated arms in the region," she said. "Naturally if they are supplied by certain people we have to protest to them as much as to those who are acquiring them."

Earlier, when a questioner said India appears to be "surrounded by a hostile buildup of a certain arc of defense," the prime minister interjected, "or offense."

This was seen as a clear sign that she views the sale of American arms to Pakistan as a potential offensive move against India, and regards American aims to get bases in the Indian Ocean-Persian Gulf region as a treat to peace on the subcontinent.

While the Indian press has been sounding the alarm about the potential dangers to this country of the sale of American F16s to Pakistan, today's statement is the clearest and most far-reaching from the Gandhi government.

The prime minister suggested that Pakistan has no "legitimate" defensive needs for such a sophisticated aircraft and said, "When you make such a tremendous jump [in weapons technology] from one era to another you obviously make problems for your neighbors."

The United States agreed to sell Pakistan the F16s last month, but it is unlikely any will be delivered until the end of this year at the earliest, and there is some speculation among informed military sources that the delivery date could be as far off as 1983 -- especially since the U.S. Air Force opposes the sale of the plane until it can fill its own requirements.

Moreover, the sale of the F16s has run into some opposition from Congress.

The U.S. offer to Pakistan was made just after the foreign ministers of India and Pakistan had met and agreed that every country had the right to acquire arms to defend itself.

Gandhi said today that what India meant by that is the "legitimate, justified" defense demands of a country. While she did not say so directly, she left the strong impression that the purchase of F16s exceeds what India considers to be Pakistan's legitimate needs.She quoted Pakistani officials as saying the planes would not be used against Soviet forces in neighboring Afghanistan and asked, "Do they need F16s against the Afghan people?"

She did not, however, say, as Indian officials usually do, that every time the United States, sells sophisticated weapons to Pakistan they are used against India.

Although New Delhi complained about the sale of American arms to Pakistan, Idia last year concluded a $1.6 billion arms purchase deal with the Soviet Union at terms so favorable that the State Department said the actual value of the weapons bought by New Delhi amounts to $8 billion.

A Western military expert said late last month that New Delhi is on the verge of making an even large arms deal with the Soviet Union, and predicted that Soviet advisers might come here to help India improve its defense production technology.

Despite a strong push over the past three months by India's influential pro-nuclear lobby, Gandhi today appeared to rule out a nuclear weapons program. Asked whether India will shift its nuclear program from peaceful uses to military application if Pakistan gains the capability to make nuclear arms, she replied:

"No. We don't believe in the deterrent theory. I don't know how it will help if we also have nuclear weapons."

In answer to an earlier question, she said, "We have declared time and time again that India uses nuclear energy for economic and other development programs."