WASHINGTON—Amid growing concern that Israel might launch a pre-emptive strike against Iran's budding nuclear program, the United States is moving ahead with the transfer to Israel of 5,000 heavy, precision-guided bombs, including 500 "earth-penetrating" 2,000-pound bombs designed for use against underground facilities.

The $319 million arms transfer, proposed by the Bush administration June 1, went ahead after Congress took no action during its 30-day review period, Jose Ibarra, a spokesman for the Defense Security Cooperation Agency, said Wednesday. The deal is being financed from this year's $2.16 billion military assistance grant to Israel.

The transfer also includes 2,500 2,000-pound Mark-84 bombs, 500 1,000-pound Mark-83 bombs, 1,500 500-pound Mark-82 bombs and live fuses. All the bombs are being fitted with the Joint Direct Air Munitions (JDAM) kit which uses inertial guidance and beacons from U.S. military Global Positioning Satellites for deadly accuracy.

"That's an arsenal for war," said Joseph Cirincione, senior associate for non-proliferation at the Carnegie Endowment for International Peace in Washington. He said any attack on Iran's nuclear facilities, clustered in three major complexes and dozens of other sites, "wouldn't be a pinprick strike; it would have to be a large-scale military airstrike that would result in large-scale casualties."

Asked Wednesday about Iran's nuclear program and the potential for an Israeli pre-emptive strike, Secretary of State Colin Powell told reporters the United States is trying to use "diplomacy and political efforts to stop this movement on the part of the Iranians toward a nuclear weapon." He did not directly address U.S. transfers of advanced munitions to Israel.

War games run at the CIA and Defense Intelligence Agency to examine the repercussions of a military strike against Iran's nuclear facilities have consistently reached a chilling conclusion: Iran would unleash a wave of terrorism against Israeli targets worldwide and against U.S. troops in the Middle East. Some 140,000 American military personnel are currently stationed adjacent to Iran in Iraq and Kuwait.

Iranian missiles have the range to hit U.S. bases in the region.

An Israeli strike, and the wider war it might touch off, also could send oil prices skyrocketing and jeopardize the global economy, analysts say.

Jay Greer, an official at the State Department's political-military bureau, which oversees arms sales and transfers, said giving the weapons to Israel "will in our view enhance U.S. national security and foreign policy interests and help maintain Israel's qualitative military edge in the region."

Asked whether the transfer makes sense amid the growing confrontation over Iran's nuclear program, Greer said, "I can't talk about that."

Israeli officials have said allowing Iran to develop nuclear weapons would threaten Israel's very existence. Last fall, Defense Minister Shaul Mofaz was reported saying that "under no circumstances would Israel be able to tolerate nuclear weapons in Iranian possession."

Iran, which insists its efforts are aimed only at developing reliable electric power sources, this week said it has begun a critical step in processing uranium into nuclear reactor fuel or nuclear bomb material: converting uranium ore, or "yellowcake," into gas. In gas form, uranium can be run through high-speed centrifuges to separate out the concentrated or "enriched" uranium.

This past weekend, the agency demanded that Iran immediately stop all uranium-enrichment processing. In reply, Iran announced Tuesday it was starting the process of converting some 37 tons of yellowcake into gas.

Military analysts say any Israeli pre-emptive strike would entail destruction not only of Iran's nuclear reactors under construction at Bushehr and Arak and the gas centrifuge facility at Natanz, but would target mobile missile launchers, strike aircraft and other weapons in order to prevent a retaliatory attack.

An attack of that scope would take two to three days of continuous airstrikes. Intelligence assessments suggest Israel would drop at least 3,000 precision-guided munitions.

Under the U.S. Arms Export Control Act, countries receiving American weapons are allowed to use them for internal security, legitimate self-defense or for "preventing or hindering the proliferation of weapons of mass destruction."

An Israeli source in Washington, speaking on condition of anonymity, said Israel purchases military equipment "on an ongoing basis" from the United States but added, "We cannot confirm any specific deals."

A Pentagon memorandum discussing the arms transfer said it would help "improve the security of a friendly country that has been and continues to be an important force for political stability and economic progress in the Middle East."