* Agenda seen as ambitious, contentious

* Efforts stepped up to revamp healthcare, energy

* Polls show public favors Democrats over Republicans

By Thomas Ferraro and Richard Cowan

WASHINGTON, April 19 (Reuters) - Barack Obama's presidency has been a wild ride for the U.S. Congress and lawmakers are bracing for more turbulence when they begin returning on Monday to tackle an array of tough issues from healthcare to energy.

In the three months since Obama took office, his fellow Democrats in Congress have overcome Republican objections and unleashed a raft of spending to try to buoy the sinking economy.

With the Senate coming back on Monday and the House in on Tuesday, following a two-week recess, the Democratic leadership in both chambers will press its advantage, while undeterred Republicans dig in their heels.

"Now the agenda gets more ambitious, and by definition more contentious," said Andrew Taylor, chairman of the political science department at North Carolina State University, noting Democrats may have trouble within their own ranks over some of the most ambitious spending proposals.

"The whole notion of deficits is going to make some Democrats uneasy," Taylor said.