By Jim Wolf

WASHINGTON (Reuters) - A panel of the National Research Council has called for construction of a ballistic missile-interceptor site in the U.S. Northeast to counter a threat that some experts say Iran could pose within years.

The current U.S. defense plan - based on a Boeing Co -run antimissile shield to be bolstered by early intercept capabilities from Europe - is "very expensive and has limited effectiveness," the panel said in a congressionally mandated report released Tuesday.

Successive U.S. administrations have spent roughly $10 billion a year to craft a layered shield against the limited number of ballistic missiles that could be fired by a country like Iran or North Korea, or to thwart an accidental launch.

It marks the Pentagon's costliest research and development effort, fueled by fears of chemical, biological or nuclear warheads.

The research council's "Committee on an Assessment of Concepts and Systems for U.S. Boost-Phase Missile Defense in Comparison to Other Alternatives" recommended that an East Coast interceptor site be set up, for instance, at Fort Drum, New York, or in northern Maine.

A similar move was called for earlier this year by the Republican-controlled House of Representatives over White House and Pentagon objections that the facility - its cost put at $5 billion by experts - was unnecessary.

An East Coast antimissile site would join a pair already in Fort Greely, Alaska, and Vandenberg Air Force Base, California. The existing sites field a combined total of 30 three-stage interceptors in silos.

Together with five additional advanced Raytheon Co-built X-band radars to track long-range missiles, an East Coast site "would more effectively protect the eastern United States and Canada, particularly against Iranian (intercontinental ballistic missile) threats, should they emerge," the 240-page report said.

Unless these and other changes, including a new interceptor missile, are incorporated, the sole shield against long-range missiles "will not be able to work against any but the most primitive attacks," it added.

LONG-RANGE STRIKES FROM IRAN, NORTH KOREA

The report said Iran and North Korea may be able to mount long-range missile strikes in the next decade or so if they press their development programs.

The United States and some other nations fear that Iran's stated plan to use enriched uranium to generate electrical power is an effort to cloak steps toward producing nuclear bombs.

The recommended improvements to the ground-based shield could be carried out within the $45 billion budget sought for the Pentagon's Missile Defense Agency from fiscal 2010 through 2016 if unnecessary missile defense programs are scrapped, the report said.

An expanded long-range U.S. shield could overtake any need, for instance, for early intercept from bases in Europe, it said.

The Obama administration's current plan, known as the European Phased Adaptive Approach, includes a projected Poland-based Standard Missile 3 interceptor to give U.S. soil an additional layer of defense by about 2021, the plan's final phase.

The panel also turned thumbs down on efforts by Northrop Grumman Corp to develop a space-based sensor system known as the Precision Tracking Surveillance System.

It would cost four times as much to buy and up to five times as much over its 20-year life cycle as the recommended X-band radar setup "and it offers less value," said the panel.

Representatives of Northrop Grumman and Boeing had no immediate comment on the report.

The Missile Defense Agency took issue with it.

"The deployed ground-based defense in Alaska and California is effective against the type of long-range missile threat we may face from North Korea and Iran," Richard Lehner, an agency spokesman, said by email.

There are no plans to augment or replace the system's existing technology with a new interceptor missile nor build any new domestic missile-defense sites, he added.

The Research Council is the main operating arm of the National Academy of Sciences and the National Academy of Engineering, which are advisors to the U.S. government on scientific and technical matters.

Representative Michael Turner, an Ohio Republican who has led the push for an East Coast antimissile site as head of the House Armed Services subcommittee on strategic forces, said the report showed President Barack Obama's approach to European missile defense was the work of a president "more focused on Russia's concerns than defense of the United States."

(Editing by Philip Barbara)