Russia will build three experimental jet airliners powered by cryogenic gas fuel of the kind normally used in space rockets, a senior official at aircraft manufacturer Tupolev said Wednesday. Vladimir Andreyev, head of the overall project, said Prime Minister Viktor Chernomyrdin had signed a decree ordering the construction of three Tupolev Tu-156 airliners in 1997. The defense and finance ministries are funding the program. Andreyev said the NK-89 engines would run on liquid hydrogen, which is ecologically much cleaner than the kerosene fuel that currently powers the world's airliners. "We have huge reserves of this gas in Russia. It is three times cheaper than kerosene," Andreyev said by telephone. "Preparatory work on this project has been going on for some time." The drawback is that a cryogenic aircraft needs four times as much fuel capacity as a normal aircraft. Earlier studies in Russia showed that using an enlarged upper-fuselage section seemed to be the best way of providing additional space for fuel tanks. The other firms involved in the project are the energy ministry, the state gas concern Gazprom, and the Kazan aircraft-engine enterprise. Test flights will take place from the airport in the central Russian city of Samara, where many Tupolev jets are built. The Tu-156 is a modification of the three-engined Tu-154 medium-range airliner.