UPDATE 2-Obama says stimulus projects under budget

(Adds Obama speech on Tuesday, details) (This report is part of a Reuters series on infrastructure)

WASHINGTON, April 13 (Reuters) - U.S. President Barack Obama said on Monday that thousands of major infrastructure projects being undertaken as part of his economic stimulus plan were ahead of schedule and under budget.

Obama, who plans to deliver what the White House called a "major" speech on the economy on Tuesday, said 2,000 new projects to rebuild U.S. highways and bridges already had been approved under the $787 billion stimulus plan that became law in February.

That plan provided $48 billion to the Transportation Department for infrastructure improvements, including $28 billion for road projects.

"By the end of next year our investment in highway projects alone will create or save 150,000 jobs, most of them in the private sector," Obama said during an appearance at the Transportation Department to plug his plan.

"What is most remarkable about this effort ... isn't just the size of our investment or the number of projects we're investing in. It is how quickly, efficiently and responsibly those investments have been made," Obama said.

"This government effort is coming in ahead of schedule and under budget," he said.

He said the 2,000th project would widen a highway and rebuild an overpass in Michigan beginning this summer, creating 900 immediate jobs and double that number by the time it was finished next year.

Obama said fierce competition for the projects had led to bids coming in under budget in many states around the country. The White House said bids have been 15 to 20 percent lower than expected on average.