WASHINGTON — President Obama called on congressional Republicans on Tuesday to take quick action to fund infrastructure projects throughout the country, arguing that failing to do so could mean huge layoffs for Americans this year.

Stepping up criticism of his opponents on Capitol Hill, Mr. Obama poked derisive fun at Republicans as he urged them to join Democrats to pass legislation that would replenish the Highway Trust Fund, which is expected to exhaust its resources by August.

“I haven’t heard a good reason why they haven’t acted,” Mr. Obama said in a speech at Georgetown Waterfront Park, overlooking the Potomac River and the Key Bridge, one of several bridges undergoing federally funded repairs after being deemed structurally deficient. “It’s not like they’ve been busy with other stuff. No, seriously!”

The president said that if Congress did not act in the next couple of months, states would have to decide which projects to continue and which to halt, ultimately placing as many as 700,000 jobs at risk.