WASHINGTON — House Republicans and Senate Democrats gained substantial support on Wednesday within party ranks for their separate plans to resolve a looming debt crisis, but the momentum seemed to be pushing both sides further from a compromise.

It was a day in which Capitol Hill seemed to operate in alternate realities: Republicans in the House sharing near universal belief that the Senate will eventually cave and accept their plan, and Senate Democrats assured that they will have the last word over the weekend and ultimately force the hand of the House.

As the House headed for a vote on Thursday, Congressional officials suggested that Senate leaders from both parties were keeping an open line for a potential compromise they could both brook. So far no such agreement appeared likely, and the Senate moved toward its own series of votes that could run through the weekend and perhaps into Monday, just one day short of the Aug. 2 date that the White House has insisted is the deadline for extending the debt ceiling for paying the nation’s bills.

Earlier in the day, at a House hearing, a representative of one of the credit rating agencies said that while the United States was unlikely to default on its obligations, its credit rating could still be cut if Congress failed to come up with a plan to reduce spending sufficiently. In the markets, investors sought alternatives to Treasury bonds and pushed down American stock prices for the fourth straight day as reverberations from the legislative impasse appeared to take a toll. The Dow Jones industrial average closed down 198.75 points, or 1.59 percent, on Wednesday; the broader Standard & Poor’s 500 stock index lost more than 2 percent.