WASHINGTON (Reuters) - President Barack Obama and Democrats will make a major push when Congress returns January 6 to renew expired benefits for the unemployed and will seek to pressure Republicans over the issue by painting them as uncaring toward the middle class.

Federal unemployment benefits will officially expire for 1.3 million out-of-work Americans on Saturday. With Congress in recess, no last-minute fix is possible.

Democrats have spent much of the holiday week criticizing Republicans for resisting an extension of the emergency jobless aid program, which began in 2008 under President George W. Bush and has been extended every year since then.

The federal benefits kick in once people exhaust their state jobless benefits, which end in many states after 26 weeks.

Senate Majority Leader Harry Reid has vowed to make an extension of the benefits the top issue in his chamber when Congress returns on January 6.

The issue is part of an economic agenda aimed at winning support from middle-class Americans. Along with the push for an extension of unemployment insurance, Democrats will also push for an increase in the minimum wage.

The renewal of unemployment benefits is expected to face opposition in the Republican-led House of Representatives, but Democrats said this week they are increasingly optimistic about gaining political traction for the issue.

Democrats have been highlighting the personal stories of out-of-work Americans about to be bumped off the unemployment rolls.

PLIGHT OF MOTHERS

An ad running on cable television by the liberal group Americans United for Change accuses Republicans of putting the interests of the wealthy above those of ordinary Americans and spoiling Christmas for the unemployed.

Earlier this week, House of Representatives Minority Leader Nancy Pelosi, a Democrat, held a conference call with reporters to highlight the plight of unemployed mothers.

The White House is also hammering the message.

"As the president has repeatedly made clear, it defies economic sense, precedent and our values to allow 1.3 million Americans fighting to find jobs to see their unemployment insurance abruptly cut off - especially in the middle of the holiday season," Gene Sperling, director of the White House National Economic Council, said in a statement.

Obama, who is spending the holidays in Hawaii with his family, on Friday telephoned Democratic Senator Jack Reed and Republican Senator Dean Heller, the sponsors of a measure that would temporarily extend the federal unemployment benefits.

Congressional Democrats, on the defensive over the botched rollout of Obama's signature healthcare law, view a focus on economic issues as a chance to improve their prospects in the midterm congressional elections in November.

Reviving a strategy that helped Obama win re-election in 2012, Democrats plan to use Republican resistance to renewing unemployment benefits and raising the minimum wage to portray them as insensitive to the struggles of middle- and lower-income Americans.

CLOCK TICKING

"The clock is ticking, not only for 1.3 million Americans who have been looking for work for longer than six months, but tens of thousands more who each week will lose their unemployment insurance if House Republican leaders don't agree to put an extension up for a vote," said Representative Sander Levin, ranking Democrat on the House Ways and Means Committee.

Democrats have seized on a comment earlier this month from Republican Senator Rand Paul that extending the unemployment benefits would be a "disservice" to those out of work by giving them less of an incentive to rejoin the workforce more quickly.

Republicans have argued that the federal unemployment benefits were always meant to be temporary and that the program would add to the deficit unless offset by reductions in spending elsewhere in the budget.

"We're not going to convince (Republicans) substantively that it's the right thing to do. We have to put political pressure on them," said Brad Woodhouse, president of Americans United for Change.

The proposal by Reed, a Rhode Island Democrat, and Heller, a Nevada Republican, would extend the federal unemployment benefits for three months.

(Reporting by Caren Bohan; Editing by Fred Barbash, Andrew Hay and Jan Paschal)