U.S. President Barack Obama talks about the economy at the Uptown Theater in Kansas City Thomson Reuters KANSAS CITY Mo (Reuters) - President Barack Obama took his criticism of congressional Republicans for confounding his agenda to a higher pitch on Wednesday, appealing to them to "stop just hatin' all the time."

Republicans in the House of Representatives are expected to vote on Wednesday to sue Obama on grounds that he overstepped his authority while implementing the Affordable Care Act, his signature health care law commonly called Obamacare.

"Stop being mad all the time. Stop. Stop. Stop just hatin’ all the time," he said of Republicans, drawing loud cheers from a raucous crowd of about 1,500 in an ornate theater in Kansas City.

"They're not happy that I'm president, but that's OK. Come on!" he said, gesturing as if to welcome lawmakers to a table.

"I've only got a couple of years left, come on, let's get some work done. Then you can be mad at the next president," he said, chuckling.

Obama has been delivering variations of the fiery stump speech all summer as he tours the country trying to motivate Democrats - and wealthy donors - to get involved in November's congressional elections.

His aim is to energize Democratic voters ahead of the elections in hopes of stopping Republicans from gaining control of the Senate, which would, when joined with a Republican hold on the House, could make it extremely difficult for him to pursue his agenda in his last two years in office.

Republicans have criticized Obama for his roadtrips, saying his time would be better spent addressing a series of domestic and foreign crises.

"President Obama should be focused on important issues facing America - not more campaigning," Missouri Republican Senator Roy Blunt said on Wednesday on Twitter.

Polls show Democrats will have a hard time holding control of the Senate in the midterm elections, while Republicans are expected to keep control of the House.

As it is, Obama has been stymied by gridlock, left to take executive actions to make changes where he has the power to do so.

Republicans argue he has overstepped his bounds, but Obama told the Kansas City audience that he was just doing his job.

"By the way, you know who's paying for this suit they're going to file? You!" Obama said.

"It’s estimated that by the time it gets resolved, I will have left office."

(Reporting by Roberta Rampton; Additional reporting by Steve Holland and Mark Felsenthal in Washington; Editing by Dan Grebler)