WASHINGTON ¨C After confronting serious technical and economic difficulties, Russia has dramatically cut back its air force program to field its first radar-evading ¡°stealth¡± fighter jet. By delaying large-scale acquisition of the Sukhoi T-50 fighter, the Kremlin is tacitly acknowledging a truth that the U.S. military learned decades ago ¡ª and that China might also learn in coming years: developing stealth fighters is hard.

But fortunately for the Russian Air Force, and unfortunately for Washington and its allied air arms that are Russia¡¯s chief rivals, Moscow has a backup plan. Instead of counting on a new stealth jet to outfit its fighter squadrons, the Russian government is buying heavily upgraded versions of older planes ¡ª an approach the Pentagon has dismissed as wasteful. It could, however, help Russia maintain its aerial edge.

The T-50, like practically all stealth aircraft before it, has proved expensive to develop, although exactly how expensive remains a closely guarded secret. Radar-evading warplanes require careful design work, extensive testing and exotic materials for their construction ¡ª all features that can double or triple their cost compared to conventional, non-stealthy planes.