DENVER - President Obama ventured 1,500 miles from Washington yesterday to sign into law a $787 billion stimulus package aimed at reviving the nation's moribund economy and "keeping the American dream alive in our time."

He signed the nearly 1,100-page American Recovery and Reinvestment Act before 250 business and community leaders gathered at Denver's Museum of Nature and Science - a setting intended to underscore the new law's role in creating clean-energy jobs. Before signing it, Obama toured a solar-panel installation on the roof.

"Now, I don't want to pretend that today marks the end of our economic problems," Obama said. ". . . But today does mark the beginning of the end, the beginning of what we need to do to create jobs for Americans scrambling in the wake of layoffs."

In the coming days and weeks, he said, he intends to launch other aspects of the strategy to "stabilize, repair, and reform our banking system" and to "stem the spread of foreclosures."

Apparently not reassured, Wall Street plunged ever lower. The Dow Jones industrials fell 297.81 points, closing less than a point above their lowest level in 51/2 years.

Obama said the stimulus law would fund record investments in education, new energy research, and new infrastructure - spending that he said would lay the foundation for the nation's economic future.

The package includes a $400 tax break for most individual workers and $800 for married couples, including those who do not earn enough to pay income taxes.

At the same time, the legislation expands safety-net programs and increases food-stamp and child-nutrition programs. There are also increased unemployment benefits and health-care access for those thrown out of work.

Republicans charged that the law was laden with pork-barrel spending and predicted it would fall short of creating the promised number of jobs while swelling the federal deficit.

No House Republicans voted for the bill.

In the Senate, only three Republicans supported it, narrowly giving it a filibuster-proof majority and handing Obama a big legislative victory within his first month in office.

Obama said the law would save or create 3.5 million jobs over the next two years.

The measure aims to spur job growth through huge investments in energy, transportation, education and health-care projects, while reviving social safety-net programs.

A little more than a third of the legislation's price tag comes from tax cuts. The rest of the costs, about $507 billion, are from spending.

In part, the new law is intended to make good on Obama's campaign pledges to upgrade the nation's aging roads, bridges and electricity grid; overhaul and computerize medical record-keeping; and develop alternative energy resources to fight global warming and reduce U.S. dependence on foreign oil.

The bill includes nearly $50 billion for roads, bridges, transit and rail, including $8 billion for high-speed rail.

Because of the stimulus package, Obama said, nearly 400,000 people will have jobs repairing roads, bridges and levees, installing broadband capability in rural areas, upgrading mass transit, and building high-speed rail.

He also cited the law's provisions to rein in soaring health-care costs, extend coverage to people who have lost their health care, and expand wellness programs.

Combined with the enactment earlier this month of a program to provide health insurance to millions of children, the new provisions mean that "we have done more in 30 days to advance the cause of health-care reform than this country has done in an entire decade," Obama said, drawing a standing ovation.

With the law's energy provisions, "we're taking big steps down the road to energy independence," he said.

"As important as the step we take today is," Obama said, "this legislation represents only the first part of the broad strategy we need to address our economic crisis."

The administration describes the stimulus plan as the first part of a three-pronged effort to attack deepening economic problems.

Administration officials last week announced the outlines of a plan to repair the teetering financial system.

Today, Obama plans to use a visit to Arizona to announce details of an initiative to stem a rising tide of foreclosures.

More than 2.3 million homeowners faced foreclosure proceedings last year, an 81 percent increase from 2007. Analysts say that number could soar to 10 million in the coming years.

Despite the president's promise to work for bipartisan support for the stimulus plan, the debate over it magnified the ideological and partisan divides in Washington.

Many Republicans criticized it as a spending bill that would not do much to right the economy.

Some economists have said it is not big enough or sufficiently focused to jolt the nation out of its economic tailspin.

In remarks to reporters aboard Air Force One, press secretary Robert Gibbs said the administration had not ruled out a second stimulus sometime in the future, although he said no plan for such a package was in the works.

Reacting to the signing, the chairman of the Republican National Committee, Michael Steele, said in a statement that "Americans looking for jobs and struggling to pay bills will be disappointed by the spending package" enacted yesterday.