Arlington, Va. ? US Airways signed deals with two jet-plane manufacturers to buy at least 170 and possibly as many as 550 regional jets from Canada-based Bombardier Aerospace and Brazil-based Embraer.

The deal includes $4.3 billion in firm orders for 85 Bombardier jets and 85 Embraer jets.

The regional jets are a linchpin of US Airways’ restructuring plan, replacing unpopular turboprop planes on short routes and more expensive mainline jets on larger routes. The airline believes the regional jets will allow it to generate more revenue and compete more effectively.

“Regional jets will allow us to replace and complement larger jet aircraft on routes with poor to marginal performance, which then can be redeployed to operate in more profitable destinations,” said David Siegel, president and chief executive officer of the Arlington, Va.-based airline.

Bombardier Aerospace said Monday the agreement included 60 firm orders for its 50-seat regional jet and 25 firm orders for its 75-seat model.

Bombardier operates a major manufacturing facility in Wichita, but it was not immediately known what effect the new order would have on that facility, which has been laying off workers during the past year.

Workers assemble RJ Regional jets at the Bombardier Aerospace plant in Montreal. US Airways signed deals with two jet-plane manufacturers to buy at least 170 and possibly as many as 550 regional jets from Canada-based Bombardier Aerospace and Brazil-based Embraer. The deal includes .3 billion in firm orders for 85 Bombardier jets and 85 Embraer jets.

Of the 85 firm orders, 36 were previously placed by GE Capital Aviation Services and committed to US Airways. The net effect increases Bombardier’s order backlog by 49 aircraft.

Bombardier said deliveries would start in the fourth quarter of 2003 and continue through the second quarter of 2005.

The Embraer order includes 85 Embraer 170 planes, with 70 seats each. The airline has the option, though, of converting the order to 76-seat Embraer 175 planes if it wishes. All the Embraer deliveries will be made by September 2006.

The Bombardier deal includes 90 reconfirmable orders, which have scheduled delivery dates but allow the customer to cancel within a specified deadline.

In addition, the agreement includes 100 options to buy a variety of Bombardier regional jets.