With time running out, an ideological battle flared in the Congress over abortion and environmental issues Thursday as negotiators launched a late push to avert a looming government shutdown.

The mood swung between optimism and pessimism as Democratic and Republican congressional leaders held a series of private meetings and public news conferences to plead their case for a budget deal that will keep the government operating beyond the midnight Friday deadline.

Senate Majority Leader Harry Reid, a Democrat, and House of Representatives Speaker John Boehner, a Republican, met for more than an hour at the White House with President Barack Obama and promised to return for another meeting at 7 p.m. EDT.

A Democratic aide said progress was made at the White House and congressional leaders hoped to work out a final compromise at the evening meeting that would keep more than 800,000 government workers in their jobs.

We are going to continue to work to get this done. It's not easy to do, but it's doable, Reid told reporters after the afternoon White House session.

Boehner said: All of us sincerely believe that ... we can get to an agreement, but we are not there yet.

The more civil tone contrasted with morning comments from the two leaders, who blamed each other for the delay in reaching a deal after negotiators worked deep into the night to narrow their differences.

Democrats said there was general agreement on the numbers in the deal, and Reid blamed the impasse on a dispute over Republican policy provisions that seek to block public funding of birth control and stymie environmental protection efforts.

In an afternoon vote, House Republicans approved a stop-gap bill to push the deadline back a week that includes $12 billion in additional spending cuts and assures Pentagon funding through September 30.

Reid called the short-term extension a non-starter in the Senate because of the spending cuts. Obama promised to veto it.

Reid said fiscal conservatives aligned with the Tea Party movement were driving the process by pushing an extreme agenda and cheering for a shutdown.

Boehner is under pressure to stand firm in the talks from Tea Party conservatives who helped fuel last year's big Republican elections gains with promises of deep spending cuts and reduced government.

If this government shuts down, and it looks like it's headed in that direction, it's going to be based on our friends in the House of Representatives, the leadership over there, focusing on ideological matters, Reid said at a morning news conference.

With the U.S. economy in the early stages of a recovery from the worst recession since the 1930s, the administration warned a shutdown could hit small business owners, applicants for home loans and workers who would be left without paychecks as the result of federal layoffs.

The investment firm Goldman Sachs estimated a government shutdown lasting more than a week could cost the economy $8 billion in missed federal spending, dragging down growth.

Vital U.S. services such as national defense, law enforcement, emergency medical care and air traffic control would continue, but national parks and museums would close and the processing of passport and a variety of loan applications would halt.

(Additional reporting by Donna Smith, David Alexander, Richard Cowan, Thomas Ferraro and David Morgan; Writing by John Whitesides; Editing by Vicki Allen)