By Steve Holland and Brendan O'Brien

WAUKESHA, Wisc. (Reuters) - Scott Walker cast himself as an anti-Washington reformer as he launched his 2016 Republican presidential campaign on Monday, vowing to fight with the same conservative conviction he used to battle unions as Wisconsin governor.

Walker rose to national prominence by defeating a 2012 recall election that grew from his challenge to the collective bargaining process for most public employee unions in Wisconsin. He won his first term as governor in 2010 and was re-elected in November.

"My record shows that I know how to fight and win. Now, more than ever, we need a president who will fight and win for America," he said.

Walker, in an announcement speech full of homespun stories about his humble roots, from flipping burgers at McDonald's to buying discount clothes, became the 15th candidate in the wide-open race for the Republican nomination.

Despite entering the campaign relatively late, Walker is among the Republican leaders in opinion polls.

His resume electrifies conservatives and is a lightning rod for criticism from Democrats unhappy with his anti-union, anti-government views. The president of the AFL-CIO union alliance, Richard Trumka, on Monday called Walker a "national disgrace."

In a sign of the tense feelings that still surround Walker in Wisconsin, a state that typically votes for Democrats in presidential elections, a small plane flew above the event site towing a banner that read "Scott Walker has a Koch problem."

Brothers Charles and David Koch use their vast wealth to advance conservative causes.

Sleeves rolled up and wearing no necktie, Walker delivered his announcement speech entirely from memory with no notes or TelePrompter.

"Instead of the top-down, government-knows-best approach we hear from politicians in Washington, we need to build the economy from the ground up in a way that is new and fresh, organic and dynamic," Walker said.

'NAME FROM THE FUTURE'

He would repeal President Barack Obama's signature healthcare law and approve the Keystone XL pipeline stalled by Obama. As governor, he has cut taxes and spending. The state budget he signed on Sunday cut $250 million from the University of Wisconsin system.

"Our big, bold reforms in Wisconsin took the power from the big government special interests and put it firmly into the hands of the hard-working taxpayers," he said.

The 47-year-old Walker has presented himself as a fresh-faced alternative to establishment favorite Jeb Bush, the former Florida governor. Bush has built a substantial financial edge and leads many polls but still faces questions about whether a third Bush presidency is in order after the White House tenures of his father and brother, and whether he could beat Democratic front-runner Hillary Clinton in the November 2016 election.

"I don't think a name from the past beats a name from the past. I think you need a name from the future," Walker told ABC News when asked about Bush in an interview broadcast on Monday.

Walker, in his speech, took some early steps to try to quiet Republican concerns about his inexperience on national security, after drawing fire earlier this year for saying his fight against the unions had prepared him for battle against Islamic State militants.

He pledged an aggressive foreign policy if elected president in November 2016. He singled out China and Russia as needing to face American muscle.

"The United States needs a foreign policy that puts steel in front of our enemies," he said.

Walker pointed to the presence of Kevin Hermening, who was among the Americans held hostage by Iran in 1979, as a reason why the Iran nuclear deal Obama is negotiating with Tehran should be abandoned.

As for Obama's declaration that climate change is a national security threat, Walker begged to differ.

"The greatest threat to future generations is radical Islamic terrorism and we need to do something about it," he said.

(Reporting by Steve Holland; Editing by Tom Brown and Cynthia Osterman)