HUNTSVILLE, Alabama — Boeing unveiled a surprise proposal to build a mobile interceptor missile in an effort to blunt Russian fears of possible U.S. fixed missile defense sites in Europe.

The idea was floated Wednesday as U.S. President Barack Obama’s administration weighs Bush-era plans to put 10 ground-based interceptors, or GBIs, in underground silos in Poland, paired with a radar site in the Czech Republic, as a hedge against Iran’s growing ballistic-missile clout. The review is to be wrapped up by the end of this year.

Boeing, which manages the hub of a layered U.S. anti-missile shield deployed in 2004, is eyeing a 21,545-kilogram interceptor that could be flown to NATO bases as needed on Boeing-built C-17 cargo planes, erected quickly on an 18-meter trailer stand and taken home when judged safe to do so.

“If a fixed site is going to be just too hard to get implemented, politically or otherwise, we didn’t want people to think that the only way you needed to use a GBI was in a fixed silo,” Greg Hyslop, Boeing’s vice president and general manager for missile defense, said in an interview at a U.S. Army-sponsored missile defense conference in Huntsville, Alabama.

A scale model showed a two-stage interceptor designed to be globally deployable within 24 hours at designated launch sites that would provide coverage for the United States and Europe.

Boeing had just started briefing the Pentagon’s Missile Defense Agency on the proposal, Hyslop said. The project could be completed by 2015 at probably less cost than had been planned for the silo-based interceptors, he said.

The Government Accountability Office reported earlier this month that military construction costs for the interceptor and radar sites could top $1 billion. U.S. intelligence officials say that by 2015, Iran will have long-range missile capability. The Polish and Czech sites are scheduled to be ready by then.

Moscow strongly opposes the possible Polish and Czech installations as a threat to its security. After Obama’s election in November, President Dmitry Medvedev threatened to base medium-range Iskander missiles near the Polish border if the United States persisted.

Boeing is not the only U.S. contractor preparing for a possible abandonment of the Polish and Czech options. Raytheon, the world’s biggest missile maker, said Tuesday that it was developing a land-based version of its existing Standard Missile-3, or SM-3, a star of U.S. missile defense from the sea, that could be used to defend Europe, Israel and elsewhere.

A reconfigured SM-3 interceptor was successfully fired by the U.S. Navy’s Aegis ballistic-missile defense system in February 2008 to destroy an errant U.S. spy satellite. Japan is co-financing and co-producing a new, more capable version. Lockheed Martin, the Pentagon’s No. 1 contractor by sales, builds the Aegis system.

A land-based SM-3 could play a role in European defense with or without GBIs in Poland, said Michael Booen, a Raytheon vice president. They could be operational as soon as 2013 if funded adequately, he said. The Pentagon has requested $50 million for its development in the fiscal year starting Oct. 1.

Army Lieutenant General Patrick O’Reilly, the head of the Pentagon’s Missile Defense Agency, hailed the SM-3 option on Wednesday and was asked about a mobile GBI.

“That would be a significant undertaking,” he said of the GBI concept after a presentation to the conference. “But we are looking for opportunities, and the SM-3 is one we focused in on because of its accomplishments.”

General James Cartwright, vice chairman of the Joint Chiefs of Staff, told the session earlier in the day that the United States had made “a couple of bad assumptions” in missile defense.

He singled out an expectation, at the heart of the U.S. rush to deploy, that “the emergence of the intercontinental ballistic missile threat would come much faster than it did” from countries like Iran and North Korea.