Casting aside partisan differences, Senate Democratic and Republican leaders said on Tuesday that they would work urgently on a package of legislation to help millions of homeowners at risk of foreclosure, with the hope of bringing a bill to the floor as early as Wednesday afternoon.

Senator Barack Obama called Thursday for tighter regulation of mortgage lenders, banks and financial houses, even as he spoke of pumping $30 billion into the economy to shield homeowners and local governments from the worst effects of the collapse of the housing bubble.

Drawing a sharp distinction between himself and the two Democratic presidential candidates, Senator John McCain of Arizona warned Tuesday against vigorous government action to solve the deepening mortgage crisis and the market turmoil it has caused, saying that “it is not the duty of government to bail out and reward those who act irresponsibly, whether they are big banks or small borrowers.”