By Doug Cameron Of DOW JONES NEWSWIRES Federal regulators on Thursday backed a revised plan allowing US Airways Group Inc. (LCC) and Delta Air Lines Inc. (DAL) to consummate a long delayed plan to swap slots at two of the country's busiest airports, though both carriers stopped short of immediately agreeing to the proposed conditions. The tentative approval requires the airlines to give up fewer slots than previously sought, and would beef up Delta's position at LaGuardia amid intensifying competition in the New York market. U.S. Airways aimed to improve its competitive position in Washington and secure rights to fly from the U.S. to Brazil. While the Federal Aviation Administration approved the plan last year, the airlines balked at the demand by regulators that they surrender a larger number of takeoff and landing slots to rivals. The Department of Transportation on Thursday backed a revised plan that would require the airlines to divest eight pairs of daily slots at Reagan National and 16 pairs at LaGuardia to low-cost rivals through a blind auction. Delta wants to transfer 42 slot pairs at Reagan National for 132 US Airways slot pairs at LaGuardia. Both airlines said they were reviewing the DOT proposal. -By Doug Cameron, Dow Jones Newswires; 312-750-4135; doug.cameron@dowjones.com