(Image Credit: Carolyn Kaster/AP Photo)

Two months after successfully marshaling public support to extend a payroll tax cut for all Americans, President Obama today attempted to do it again.

"Allowing this tax cut to expire would make people's lives harder right now.  It would make their choices more difficult.  It would be $40 less for groceries to feed your kids.  It would be $40 less for the medications you depend on, $40 less to cover bills and the rent, $40 less to take care of an elder parent or to donate to a church or a charity," Obama said in a speech from the South Court Auditorium at the White House.

"Call, tweet. Write your congressman, write your senators.  Tell them:  Do not let up until this thing gets done.  Don't let taxes go up on 160 million  working Americans."

Obama was flanked by a group of supporters who were among the tens of thousands that spoke out online and on social media in December to pressure Congress to compromise, securing a temporary deal to extend the tax cut through the end of this month.

Now taxes are set to rise again on 160 million Americans unless lawmakers act, and congressional negotiators remain at impasse.  The administration estimates the tax cut would save a family making about $50,000 a year $40 per paycheck.

Obama said there are "hopeful signs" that an extension of the tax cut will be achieved. But he warned the audience not to take anything for granted.

"We've got to keep on making sure that the American people's voices keep breaking through until this is absolutely, finally, completely done," he said. "Until you see me sign this thing, you've got to keep on speaking up. Until you see that photograph of me signing it at my desk - you know, make sure it's verified, certified."

The White House hopes to spark a social media blitz, with average Americans concerned about their paychecks taking to Twitter - using the #40dollars hashtag - or posting their opinions on Facebook or the White House blog.

Meanwhile, congressional negotiators have 14 days to work out the fine print of a deal.

At issue is how to offset the cost of the tax cut and whether to extend unemployment insurance benefits and deal with the Medicare "doc fix" at the same time.

House Republican leadership Monday proposed as a last resort passing the payroll tax cut extension alone, through the end of the year, and dealing with the other issues separately.

But Democrats are reluctant to consider the items separately, believing that doing so would compromise passage of all the items.

White House press secretary Jay Carney signaled Monday that the administration backs a legislative solution to the payroll tax cut, unemployment insurance and "doc fix" all at once. "We are willing to work with them to offset [costs] in a responsible way," Carney said of Congress.