Leaders of America’s top unions are to convene today in Las Vegas to debate proposals for a radical restructuring of the organization that has been at the heart of the labor movement for half a century, the AFL-CIO.

“It’s a dramatic challenge that’s been made to the existing structure of the AFL-CIO by some of its largest affiliates,” said a professor in the school of management and labor relations at Rutgers, Robert Angelo.

One of the most sweeping reform plans, put forward by the president of the Service Employees International Union, Andrew Stern, would allow unions to boost their organizing efforts by reducing their dues payments to the AFL-CIO by as much as 50%. The redirection of funds could force the labor group’s Washington headquarters to cut its staff sharply.

The labor movement has experienced a perfect storm of sorts in recent years as membership rolls have dwindled and labor’s political allies in the Democratic Party have suffered defeat after defeat at the polls. The loss last November of the party’s presidential nominee, Senator Kerry, despite an unprecedented effort to get out the union vote, has added to the impetus for change.

While the push for change at the AFL-CIO was afoot well before last year’s election, a spokesman for Mr. Stern acknowledged that Mr. Kerry’s defeat appears to have brought new support for all kinds of reform initiatives.

“We played through the election cycle with certainly the hope of a Kerry presidency,” said the spokesman, Benjamin Boyd. “With a Bush presidency, it’s certainly more critical that changes be made to a movement that is not in a position to defend workers.”

Under pressure from the Service Employees and from the Teamsters, the president of the AFL-CIO, John Sweeney, said last week that he would support a cut in dues paid to the umbrella group. However, he did not say how large a cut he would endorse.

“We’ll be pushing ideas for change that grow out of this discussion and debate,” Mr. Sweeney, who is seeking re-election, said during a conference call with reporters last week. “The bottom line is how we can make a real difference in the lives of working families.”

The struggle will play out over the next few days as leaders of the AFLCIO’s 58 member unions gather in Las Vegas for a closed-door meeting of the federation’s executive council. A smaller group, the executive committee, met yesterday and were scheduled to meet again tomorrow.

Many old-line industrial unions, such as the International Association of Machinists, are resisting Mr. Stern’s campaign. Some of his proposals – such as a more aggressive campaign targeting Wal-Mart – enjoy widespread support, while others have caused division. One of the most controversial is a suggestion that the AFL-CIO be given the authority to merge small unions into larger ones.

One labor official said in an interview that voluntary mergers might be wise in some cases, but that eliminating workers’ ability to choose between unions was unwise and unlikely to be productive.

“The Wobblies tried that about 100 years ago and it didn’t go very far,” the union official said.

The stakes in the current dispute are high. The leader of a hotel workers’ union that supports a restructuring, John Wilhelm of Unite Here, has said he might mount a challenge to Mr. Sweeney during a union election this summer. Mr. Stern has said his union and others will bolt from the AFL-CIO if organizing efforts are not given a higher priority. That would be a crippling blow to the federation, since the Service Employees is one of the few unions to increase its membership in recent years.

Last year, union membership stood at 15.5 million, or 12.5% of all employees, according to the Bureau of Labor Statistics. The percentage of workers belonging to a union has declined steadily since 1983, when it stood at 20.1%.

The structure of the AFL-CIO, which gives the older, small unions power disproportionate to their numbers, is also an obstacle to change.

“We’re not in control of the agenda,” said Mr. Boyd of the Service Employees. “We’ll see where we net out by Friday of this week on real change versus cosmetic change.”

In some respects, the proposals for belt-tightening at the AFL-CIO resemble the wave of staff reductions and restructuring that have taken place in corporate America during the past two decades, often over the loud objections of labor groups.

However, Mr. Stern’s plan could also have consequences that go far beyond the staffing at AFL-CIO headquarters. A large-scale redirection of union funds toward organizing would divert some of the millions of dollars that the unions have pumped into Democratic Party coffers and get-out-the-vote efforts.

The new chairman of the Democratic National Committee, Howard Dean, is scheduled to address the labor leaders this morning. One union official attending the meeting at Las Vegas said labor’s get-out-the-vote campaign in the last election was enormously successful. The only flaw, he said, was that there weren’t enough votes to get out.

“We can’t do a better job unless we get more members,” he said. “I think there was a sort of universal consensus about that.”