WASHINGTON — John McCain's campaign, trailing top Republican rivals in money and polls, is undergoing a significant reorganization with staff cuts in every department, officials with knowledge of the shake-up said today.

Some 50 staffers or more are being let go, and senior aides will be subject to pay cuts as the Arizona senator's campaign bows to the reality of six months of subpar fundraising, these officials said.

They spoke on condition of anonymity because the plans have not been made public. An afternoon conference call was scheduled to announce the results of second-quarter fundraising.

Once considered the front-runner for the GOP nomination, McCain came in third in the money chase behind Mitt Romney and Rudy Giuliani, raising $13.6 million in the first three months of the year. He is struggling to reach that total in the second financial quarter, and wasn't expected to match it.

Officials said the fundamental leadership of the campaign will not change; Terry Nelson, a veteran of President Bush's winning 2004 campaign, will remain campaign manager but may volunteer his time instead of drawing a salary.

Nelson declined to comment, and Brian Jones, the campaign's communications director, did not immediately respond to requests for comment.

At its peak, McCain's payroll covered 150 staffers; this is the second round of layoffs.

The financial difficulties have fueled speculation that McCain would drop out of the race but he dismissed that notion Thursday, calling it "ridiculous." He argued that voters won't start paying close attention until the fall, and said: "I don't know why I would even remotely consider such a thing in the month of June, or July."

Six months before primary voting begins, McCain is struggling for some semblance of momentum.

His popularity among Republicans has dropped since the start of the year. He has become intimately linked to the unpopular Iraq war, and, in recent weeks, he's drawn criticism from already wary conservatives for his support of Bush's immigration reform bill. He declined to participate in an early test of organizational muscle in the leadoff state of Iowa this summer, and, he's fighting the perception that he's yesterday's candidate.

McCain's support in national polls has slipped. He is in single digits in some surveys in Iowa and South Carolina, trailing Giuliani, the former New York mayor; Romney, the ex-governor of Massachusetts, and Fred Thompson, the actor and former Tennessee senator who's not yet in the race officially.