Backed by growing global demand for small, energy-efficient aircraft, Mitsubishi Heavy Industries Ltd. officially decided last month to enter the promising market.

Analysts forecast as many as 4,500 sales of regional jets, which have 60 to 90 seats, in the next 20 years amid rising fuel costs and improving transportation among regions.

But industry sources expect Mitsubishi Heavy, a newcomer to the regional passenger jet sector, to face extremely harsh competition, especially as the market is currently dominated by Canada's Bombardier Inc. and Brazil's Empresa Brasileira de Aeronautica SA, better known as Embraer.