By Bradley Perrett, European aerospace & defence correspondent SINGAPORE, Feb 26 (Reuters) - Boeing Co (BA) on Tuesday launched its latest attempt to revive flagging sales of the 747 wide-body airliner, offering a new version of the jumbo jet that would fly further and make less noise. "Based on increasing customer interest, Boeing is developing this new family of 747 airplanes and is now offering them to airline customers," Boeing said in a statement issued at the Singapore air show. "The 747-400XQLR could enter service in early 2004, depending on customer demand." Boeing developed the 747 in the late 1960s, upgraded it in the late 1980s and then watched its sales slow in the late 1990s as airlines turned to smaller aircraft that could match its long range. Beaten at the top end of the market by the 555-seat A380 superjumbo being developed by Europe's Airbus SAS (EAD)(EAD), Boeing has proposed a succession of progressively less radical make-overs of the 416-seat 747. On Tuesday it said it was now offering it with more fuel capacity and refined, quieter engines from General Electric Co (GE). The 747 is already the fastest subsonic airliner and the new version would be a little faster again, Boeing said. In a teleconference with reporters in the United States, Boeing said it plans to deliver its first 747-400XQLR in March 2004, assuming it can book its first order by June 2002. "We are not in a position to launch the airplane," said 747 brand manager Bill Droppleman. "We are offering the airplane." ROLLS-ROYCE OFFER British aero-engine company Rolls-Royce Plc (RR) said it wanted to supply an advanced new engine for the 747-400XQLR that would be even quieter and would use less fuel, lowering costs and further extending the plane's range. "We have with the Trent 600 the only modern engine in that thrust class (required by the 747-400XQLR)," chief operating officer John Cheffins told reporters in Singapore. "We are offering it to Boeing and they are very interested." Boeing is also discussing new, quieter engines with United Technologies Corp (UTX) unit Pratt & Whitney, Droppleman said in the teleconference. "We are having discussions with both of them. We're not near as far along with either," he said. "GE has a package we understand." None of the companies involved issued financial details, but each is proposing relatively low-cost developments of current products. Reducing the 747's noise would be no mere publicity measure for Boeing. Pressured by residents near airports and their politicians, most airlines are extremely keen to minimise noise and will pay more for aircraft that cause less bother. The 747, originally considered quiet, has been left behind by by newer planes that make much less noise on take off and landing. It is now regarded as one of the noisiest Western airliners. 747 COMMITMENT Some analysts have suspected that Boeing could soon close its 747 production line because of the weak sales and the repeated failure of earlier proposed improvements to excite airlines. Such doubts about a plane's future can become self-fulfilling prophecies because potential customers worry the resale values of a particular model will depreciate if it goes out of production. At the Singapore air show, Boeing's senior vice president for sales, Larry Dickenson, stressed the company's commitment to the model. After detailing the new version's potential, he said: "I'd also like to make one more promise today -- that we will stand by the 747 family."