WASHINGTON — President-elect Barack Obama on Saturday pledged to launch the biggest public works program since the construction of the interstate highway system in the 1950s as part of his plan to create millions of new jobs and stem an economic tailspin that is growing worse by the day.

"We need action — and action now," Obama said in a weekly address broadcast on radio and posted as a YouTube video.

His comments came the day after the government announced that 533,000 jobs had been lost in November — the worst monthly job loss report in 34 years. The address marks the latest effort by the incoming president to shape events and build momentum for his agenda weeks before he takes office.

Obama aides and Democratic lawmakers hope that a new economic stimulus plan, which could cost as much as $700 billion, will be passed by Congress in January so that Obama can sign it into law within hours or days of his inauguration on Jan. 20.

The plan, as Obama laid it out on Saturday, would include massive investments in roads and other infrastructure programs reminiscent of President Dwight D. Eisenhower's highway program that employed millions of people and cost tens of billions of dollars. Obama said he would compel states to move quickly on construction projects or risk losing the help from the federal government.

"We'll invest your precious tax dollars in new and smarter ways," he said, and "we'll set a simple rule — use it or lose it. If a state doesn't act quickly to invest in roads and bridges in their communities, they'll lose the money."

Obama said his plan would include a push to make federal buildings more energy-efficient by installing new heating systems and energy-saving light bulbs, a plan he said would save billions of taxpayer dollars and "put people back to work."

Additional provisions would upgrade public school buildings, enhance broadband technology and create a system to ensure Americans have access to electronic medical records.

His comments reflected the growing belief among his top advisers and Democratic leaders on Capitol Hill that the fast-declining economy and the continued loss of jobs require a massive spending program — even if it means swelling the national debt.

Since the recession began a year ago, about 2 million jobs have been lost. Obama has said that his plan would aim to create 2.5 million new jobs by 2011.

Americans will be hearing a lot from Obama this weekend. He is scheduled to sit for an hourlong interview with NBC's Meet the Press, to be broadcast today, and has scheduled a news conference for this afternoon.