WASHINGTON » When Wisconsin’s governor, Scott Walker, began his crusade against collective bargaining by public employees, his state’s unions seemed woefully outmatched. But Wisconsin’s beleaguered labor movement woke up and mobilized, through e-mail blasts, phone trees and Facebook, getting tens of thousands of supporters to rally in Madison against the legislation and surprising itself that it could muster such a show of force so quickly.

For now, the two sides are at a stalemate, with protesters still swarming the Capitol and Democratic senators hiding in Illinois to deny the Republican majority the quorum needed to pass Walker’s bill. Meanwhile, governors in other states, most notably New Jersey and Ohio, have gone on the offensive against labor, deriding teachers’ unions, tenure and generous pensions.

Organized labor has been on a long decline, but the recent attacks against it in Wisconsin and elsewhere have had a surprising result — they have energized the nation’s unions. Instead of just playing defense to protect benefits and bargaining rights, labor leaders are plotting some offense, with several saying Walker may have unwittingly nurtured a comeback by unions.

As the Wisconsin showdown has unfolded, several recent national opinion polls have shown strong public backing for unions. And labor leaders say public awareness, especially among younger people, of what unions do has clearly increased.

"The challenge for us is to take this moment and turn it into a movement," said Randi Weingarten, president of the American Federation of Teachers. She acknowledged that she was not sure whether labor could accomplish that, but union leaders are quietly forging strategies to propel labor’s cause beyond the immediate statehouse battles.

At the AFL-CIO’s winter meeting in Washington last week, labor leaders were laying plans to enlist some of the thousands of union members who have protested in Madison; Indianapolis; Columbus, Ohio; and elsewhere to work in the campaign by the Communications Workers of America to unionize 20,000 T-Mobile workers.

Similarly, union leaders want to harness some of this activism as well as the newfound cooperation between private sector and public sector unions to get hundreds of organizers to help unionize 45,000 airport security employees.

And the Service Employees International Union is seeking to channel the spirit and energy of Wisconsin into its immense new campaign in 15 cities, including Chicago, Detroit and Houston, to unionize tens of thousands of low-wage private sector workers as well as to get them to fight foreclosures and budget cuts. Mary Kay Henry, the SEIU’s president, said she hoped the protests in Wisconsin and Ohio would give a particular lift to her union’s efforts in Milwaukee and Cleveland.

But many labor experts say that talk of a union resurgence is overly optimistic and that labor leaders may be flattering — even deluding — themselves.

Harry C. Katz, dean of the Cornell University School of Industrial and Labor Relations, said many powerful forces militate against a labor rebound. High unemployment, globalization of manufacturing and corporate opposition will continue to drag down unions, especially private sector ones, he said. In the public sector, mounting budget deficits and newly empowered Republican leaders are potent threats.

"I would worry more about whether unions can hold off the onslaught than whether they can get a big snapback," Katz said.

Before Wisconsin erupted, things were looking grim for unions. They had achieved few major gains during President Barack Obama’s first two years in office. And even though unions spent huge amounts to elect Democrats last November, Republicans rolled to victory, including in Wisconsin and Ohio, traditional labor strongholds. Several prominent corporations, including Harley-Davidson, had pressured their unions into accepting humbling contracts that called for a far lower pay scale for new employees.

And public sentiment toward unions and the percentage of private sector workers who belonged to unions had slid to new lows, with many people blaming the auto workers’ generous contracts for pushing Detroit’s automakers toward collapse.

Stopping that downward momentum, let alone reversing it, is a huge challenge. On Thursday, Obama dealt labor another blow by agreeing to let Mexican trucks carry goods across the border, a move the Teamsters have long opposed.

Phil Kerpen, vice president for policy at Americans for Prosperity, a conservative advocacy group that backs Walker, said most workers see little value in joining a union.

"It’s very unlikely that you’ll see any resurgence in private sector unionization," he said, "because most workers are worried that unions will put their employer out of business and they’ll lose their job." Indeed, in today’s tough economic environment, unions are often in the position of negotiating concessions rather than raises and better benefits.

If Walker emerges victorious in his battle with labor, he may well claim the mantle of President Ronald Reagan, who crushed the air traffic controllers’ union in 1981 after thousands of workers walked off the job illegally. But if unions somehow succeed in blocking his effort to cripple collective bargaining, they will have arguably won their biggest, most visible victory in years — and that, they hope, will give them some real momentum.

"This might be the beginning of a real resurgence for labor," said Gerald McEntee, president of the American Federation of State, County and Municipal Employees.