The versatile, carrier-based "Super Hornet" attack jets are the biggest military aviation programme in both Boeing's and the US Navy's history. The planes, to be built under an initial full-scale production deal are the first of up to 548 that the Navy hopes to buy in the future.

The US Navy said in February that virtually new version of its older F/A-18C fighter had passed flight tests with the highest marks and that the Super Hornet would be ready for deployment in two years.

Defence Secretary William Cohen in April urged Congress to allow the unusual, multi-year production deal for Boeing, saying that the five-year programme would save more than $600 million by skipping annual contracts.

Boeing will perform 60 percent of the work on the planes in St Louis, with its partner Northrop Grumman Corp taking on the remaining 40 percent in Los Angeles. All 222 planes are to be delivered by September 2006.

Boeing officials, who had been anticipating this announcement for some time, said the order would trigger investment in its St Louis facilities and workforce.

"We and our suppliers now have a more predictable work load which helps us plan the work better. We are able to invest more in processes and production improvements that will pay off in the future," said Defence Department spokeswoman Jo Anne Davis.

Shortly before the Pentagon announcement, Boeing had announced plans to sell off a parts fabrication unit in St Louis, employing 1,700 of its 17,500 local workers, in an effort to streamline operations.

That unit, currently running at 40 percent of capacity, might expand under a new owner that could use it to build parts for other manufacturers as well as Boeing, Davis said.

Although the Congressional General Accounting Office has raised some concerns about what it calls noise and vibration problems with the new carrier jets, the Navy has assured lawmakers that it is fixing the problem.

"There is some noise and vibration that is a very slight issue, but it's eminently fixable," Davis added. New Defence Department fighter programmes have sparked major questions and cost criticisms in Congress.

The F/A-18E/F is being bought at the same time that the Air Force is preparing to build its expensive new radar-avoiding F-22 "stealth" fighter and the Pentagon is planning a Joint Strike Fighter to be shared by the Air Force, Navy, Marine Corps and British Royal Navy.