BAGHDAD, Feb. 11 — After weeks of internal debate, senior United States military officials on Sunday literally put on the table their first public evidence of the contentious assertion that Iran supplies Shiite extremist groups in Iraq with some of the most lethal weapons in the war. They said those weapons had been used to kill more than 170 Americans in the past three years.

Never before displayed in public, the weapons included squat canisters designed to explode and spit out molten balls of copper that cut through armor. The canisters, called explosively formed penetrators or E.F.P.s, are perhaps the most feared weapon faced by American and Iraqi troops here.

In a news briefing held under strict security, the officials spread out on two small tables an E.F.P. and an array of mortar shells and rocket-propelled grenades with visible serial numbers that the officials said link the weapons directly to Iranian arms factories. The officials also asserted, without providing direct evidence, that Iranian leaders had authorized smuggling those weapons into Iraq for use against the Americans. The officials said such an assertion was an inference based on general intelligence assessments.

That inference, and the anonymity of the officials who made it, seemed likely to generate skepticism among those suspicious that the Bush administration is trying to find a scapegoat for its problems in Iraq, and perhaps even trying to lay the groundwork for war with Iran.