The Bush administration says that it has agreed to sell Pakistan advanced missiles designed to be launched from ships and submarines.
Harpoon's makers say it is a 'most successful' anti-ship missile
It says that it has also agreed to sell $375m worth of related equipment.
In a notice to Congress, which has to agree the proposal, the Pentagon said the sale would significantly upgrade Pakistan's existing weapons systems.
It said that the security of the US would be improved by aiding what a "key ally in the war against terror".
The proposed sale is being dealt with by The Pentagon, which handles most such deals on behalf of the US government.
The Pentagon Defence Security Cooperation Agency said in a notice to Congress that 50 Harpoon missiles sold to Pakistan would be for launch from submarines, 50 from surface ships and 30 by air.
However, officials stress that the deal is far from being completed, and could be vetoed by Congress.
The US-Pakistan deal will not be welcomed by India
"This proposed sale will contribute to the foreign policy and national security of the United States by helping to improve the security of a friendly country that continues to be a key ally in the global war on terrorism," a Pentagon statement said.
The US lifted restrictions on arms sales to Pakistan last year, when it announced an expansion in two-way defence trade, missile-defence cooperation, technology transfers and weapons co-production.
The restrictions were put in place in 1990, but lifted after The Pentagon said Pakistan had "demonstrated its willingness to fight terrorists", especially in Waziristan.
Correspondents say Pakistan had originally requested a much larger package, but had downgraded the amount, saying it could no longer afford it after last year's earthquake.
Harpoon uses a satellite-aided navigation system which The Pentagon says will "significantly reduce the risk of hitting non-combatant targets, thus improving Pakistan's naval operational flexibility".
The Pentagon says that Pakistan will use the new equipment on maritime surveillance aircraft, surface ships and submarines
Pakistan has fought three wars with India since both counties won independence in 1947.