TEGUGICALPA, Dec 9 (Reuters) - Incoming Honduran President Xiomara Castro received a potential boost on Thursday when an opposition party offered to support her party in presiding over the next Congress, where initial election results suggest she may lack control. Preliminary results of last month"s election suggested that Castro"s leftist Liberty and Refoundation Party (Libre) would win about 50 seats and its main allies would muster about 10 more in the new 128-member Congress, leaving them short of a majority. Still, Yani Rosenthal, leader of the center-right Liberal Party, which is tipped to win around 22 seats, said his party was willing to vote for a Libre lawmaker to head Congress, possibly setting the scene for broader cooperation. Rosenthal, who ran unsuccessfully for president this year, said the offer was not tied to any conditions. It poses complications, however, because Salvador Nasralla, Castro"s political partner who controls Libre"s main allies, noted that one of his 10 prospective lawmakers was due to head Congress under a deal previously forged with her. Projected to be the second-biggest force in Congress with 44 seats, ahead of the Liberal Party, is the conservative National Party of outgoing President Juan Orlando Hernandez. Castro is set to take office in January.