WASHINGTON — The downsizing of Senator McCain’s presidential campaign is coming at an opportune time for Fred Thompson, the former Tennessee senator who is likely to jump into the race officially any day now and seeking to build a campaign staff in the early primary states.

Struggling with a shortage of cash, Mr. McCain’s campaign announced last week that it was laying off dozens of staff members, including about half of his paid team in Iowa and New Hampshire.

While there is no evidence of an outright pillaging of Mr. McCain’s departed aides, Republican sources in those states say Mr. Thompson’s emerging campaign is the likeliest landing spot. Aside from Mr. Thompson’s obvious need for staff — assuming he enters the race — the two are closely aligned ideologically, and Mr. Thompson even endorsed Mr. McCain when he sought the White House in 2000.

Aides to Mitt Romney say the former Massachusetts governor has already filled his paid staffing positions in Iowa and New Hampshire, and while Mayor Giuliani is still hiring, his campaign said they have not yet signed any of Mr. McCain’s former staffers. “I think a staff person working for McCain would be comfortable working for Thompson, as opposed to Rudy,” an unaffiliated Republican consultant in Iowa, Robert Haus, said.

The Arizona senator, once considered the front-runner for the Republican nomination in 2008, made the moves after a second straight lackluster fund-raising quarter. Mr. McCain finished behind Messrs. Romney and Giuliani, and while he has raised more than $24 million for the year, he has only $2 million on hand, indicating an unsustainable rate of spending. And in an embarrassing disclosure that added insult to Mr. McCain’s injury, a long-shot Republican contender who has barely appeared on most national polls, Rep. Ron Paul of Texas, said this weekend that after a strong second quarter, he had more money on hand, $2.4 million, than did Mr. McCain.

For Mr. McCain, who has planned for another presidential bid for years, the contrast with Mr. Thompson could not be starker. The “Law & Order” star, who left the Senate in 2003 after serving less than two full terms, has professed to have no lifelong presidential ambition, and he began seriously considering a run for the office only in recent months. Mr. Thompson formed a “testing the waters” committee in May , and he has given speeches recently in New Hampshire and South Carolina. He has hired a Midwest coordinator, Andrew Dorr, a veteran of Iowa campaigns who has been fielding résumés and working the phones in the site of the first caucus over the last week.

Mr. Thompson does not have paid staff in New Hampshire yet, but his top boosters there include a former state representative, Daniel Hughes, and a longtime political consultant, William Cahill. They are just waiting for the signal, Mr. Hughes said yesterday.

“I wish we had a green light to go and organize and do our thing,” he said. Mr. Hughes organized Mr. Thompson’s first appearance as a potential candidate in the state late last month, at a fund-raiser for Republicans in the state Senate.

“There were a lot of McCain people there,” Mr. Hughes said. “A lot of his volunteers are looking around.”

But while rival campaigns like to hint that Mr. McCain’s endorsements are soft and his supporters may be looking elsewhere, few appear to be jumping ship at the moment.

Days before his fund-raising disclosure, a national Republican Party committeewoman in New Hampshire, Nancy Merrill, announced that she was leaving her post to work for Mr. McCain full time. When the news of Mr. McCain’s money troubles and staffing cuts hit, the state party chairman, Fergus Cullen, said he called Ms. Merrill to ask if she was reconsidering. The response was quick and unequivocal: no way. While Mr. McCain’s outlook appears bleak now, history offers some hope. President Reagan struggled during his second bid for the presidency in 1980, and as recently as 2003, Senator Kerry trailed badly in fund-raising and in the polls before overtaking Howard Dean and John Edwards to win the Democratic nomination.

Exactly when Mr. Thompson will officially join the fray remains unclear, but his supporters are at the ready. “I wouldn’t be surprised if I got a call tomorrow,” Mr. Hughes said.

Political strategists say he has played the waiting game well, allowing the support and speculation to build and watching as he has jumped to the top of some polls without even entering the race.

Mr. Thompson’s unofficial status also holds off the increased press scrutiny that comes with being a candidate, but that may not last much longer. Articles have begun to crop up scrutinizing his past as a Washington lobbyist and his record on abortion, a key social issue.

And his backers may get antsy if he waits much longer. As Mr. Hughes put it: “People like me are going to say, ‘Fish or cut bait. It’s time to go.'”