House Democratic leaders worked furiously on Thursday to secure the final votes for weekend approval of a sweeping healthcare overhaul as President Obama threw his weight behind the lobbying effort and Republicans dug in against the health plan. Democratic vote counters said they did not yet have the necessary 218 confirmed supporters. But they said they were confident they would exceed that total in time for a landmark vote set for Saturday on the $1.1 trillion, 10-year health plan that many Democrats have sought for years. Readying for the first floor test of legislation months in the making, top Democrats appealed to undecided lawmakers while trying to quell resistance from Hispanic House members worried the measure was too punitive regarding illegal immigrants and anti-abortion lawmakers who fear that public money could be funneled toward abortions.