The Bush administration rewarded Pakistan, an improbable ally in the war on terrorism, with a promise Friday that it could buy sophisticated U.S.-built F-16 warplanes (search). Pakistan's nuclear rival, India, immediately complained the sale would threaten its security.

The sales would represent a shift in policy after years of sanctions and harsh rhetoric from Washington over Pakistan's nuclear ambitions and what U.S. administrations have seen as tolerance for Islamic extremism. Since the Sept. 11, 2001, terror attacks, however, Pakistan (search) has become an important partner in hunting suspected terrorists and cracking down on anti-American extremists.

Mindful of the fragile balance of power in South Asia, the administration also gave a green light to India for its own purchase of sophisticated weapons.

State Department spokesman Adam Ereli said the administration sent reports to Congress on Friday describing proposals to sell armaments to both Pakistan and India (search). Congress must sign off on the sensitive technology export.

Ereli said, "We are looking to improve security and improve prosperity and improve development of the entire region as a whole."

"Part of that is a decision to begin negotiations with the Pakistani government and Congress to sell F-16s to Pakistan and to respond favorably to a request for information from India for the possible sale of multi-role combat aircraft," he said.

U.S. defense companies are now "free to talk to India about what they have to offer, and it will be up to India to decide what it wants," to buy, Ereli said.

The move allows Pakistan to finally move ahead on planned purchases of two dozen F-16s dating to the 1980s, before the United States blocked the sale because of Pakistan's increasingly obvious drive to build nuclear weapons.

There is no limit on future sales to Pakistan, a State Department official said on condition of anonymity.

Pakistan's information minister, Sheikh Rashid Ahmed, called the decision a "good gesture by the United States" and said the transaction would ease anti-American sentiment in the Islamic nation.

"This will fulfill our defense requirements," he said. "We had been lagging behind (India) in conventional weapons. This will improve the situation."

Secretary of State Condoleezza Rice (search) said she discussed sales of F-16s to both Pakistan and India during back-to-back visits to those countries earlier this month. Rice chose not to announce the Pakistan decision on that trip in part to avoid angering India.

India and Pakistan have fought three wars since the former British colony was partitioned in 1947 into predominantly Hindu and predominantly Muslim states.

President Bush tried to head off Indian worries with an early morning phone call to Indian Prime Minister Manmohan Singh. Calling from his ranch in Crawford, Texas, Bush told Singh that the administration was moving ahead with the sale, White House spokeswoman Dana Perino said.

At the same time, Bush told Singh that the United States was responding to India's request for information on its own future warplane purchases, Perino said.

The United States reassured India that it had the administration's blessing to buy F-16s, or perhaps F-18s. India is contemplating a multibillion dollar purchase of fighter planes, including U.S.-built or foreign-made aircraft.

The United States has sold a variety of weaponry to India since lifting a ban on arms sales three years ago that had been imposed after an Indian nuclear test. Last year, in a move seen as a coup for India, the administration gave the go-ahead for Lockheed Martin (search) to give India information for prospective sales of F-16s.

Singh told Bush that sales to Pakistan would endanger security in the region, and expressed "great disappointment" over the decision, Sanjaya Baru, the prime minister's spokesman said.

New Delhi is worried that arming Pakistan with the advanced jet fighters would tilt the military balance in the region and could adversely affect peace talks between India and Pakistan.

The F-16 sale to Pakistan is meant to remove a persistent irritant in U.S.-Pakistani relations. Pakistan struck a deal with the United States to buy the nuclear-capable F-16 fighter jets 15 years ago, but the agreement was scrapped in the 1990s when Washington imposed sanctions.