Rudolph Giuliani’s decision to largely abandon the early voting state of New Hampshire and concentrate his efforts on the Florida primary three weeks later reflects an uncomfortable truth for the former New York mayor: The more he campaigned in the Granite State and the more he spent on advertising there, the more his poll numbers dropped.

Mr. Giuliani appears to be making a virtue of necessity by sounding the retreat in New Hampshire, where he continues to be outgunned by the Republican front-runner there, Mitt Romney, and where he has been beaten into second place by the resurgent campaign of Senator McCain.

He must now be sure to win Florida on January 29 to capture its large cache of delegates, as part of a strategy that sees him withdrawing from the smaller early states in favor of states such as New York, California, and Florida, which send large numbers of delegates to the nominating convention.

However, the wisdom of that strategy was cast in doubt yesterday by the latest poll in Mr. Giuliani’s home state of New York showing the mayor’s lead over his nearest Republican rivals cut by 11 points.

Mr. Giuliani now leads 37% to Michael Huckabee’s 12% in New York, with 11% for Mr. McCain, 7% for Fred Thompson, and 5% each for Mr. Romney and Rep. Ron Paul, according to a new Quinnipiac poll.

A similar poll on October 17 showed Mr. Giuliani enjoying a 37-point lead over his nearest rival, Mr. Thompson, a former Tennessee senator.

“Mayor Giuliani is on top of the Republican field, but losing some steam,” the director of the Quinnipiac University Polling Institute, Maurice Carroll, said in a statement.

Mr. Giuliani’s slide in New York comes hot on the heels of a Rasmussen poll at the end of last week showing him in third place in Florida behind Messrs. Huckabee and Romney after easily leading the field since September.

Although the mayor was never likely to win New Hampshire, where Mr. Romney has invested a great deal of time and money, Mr. Giuliani had sought to prevent the former Massachusetts governor from gaining national momentum with an easy win there.

Mr. Giuliani’s gambit of leaving Mr. Huckabee to diminish Mr. Romney’s early lead in Iowa, and thereby put the New Hampshire result in doubt, appears to have backfired.

The former Arkansas governor is now not only the favorite to win Iowa but is quickly gaining ground on Mr. Giuliani both in New Hampshire and in national polls, which until early December showed the mayor enjoying a substantial lead.

The Giuliani campaign is now sharply cutting advertising on Boston television stations aimed at neighboring New Hampshire. Figures reported by the Nashua Telegraph tell the scale of his retreat.

Having spent $102,745 on advertisements on WHDH on December 5, Mr. Giuliani slashed spending to $40,700 on December 11. Over the same period, the Giuliani ad spending on WFXT dropped to $20,000 a week from $67,000. On WBZ and WSBK, the Giuliani campaign has halved its spending. And the $20,300 worth of airtime bought on WLVI on December 5 was canceled six days later.

According to Campaign Media Analysis Group, Mr. Giuliani spent $1.7 million in New Hampshire between November 10 and December 9. During the same period, Mr. Romney spent $1.3 million and Mr. McCain $1.2 million.

Despite being the biggest spender on television in New Hampshire during that period, Mr. Giuliani saw his support fall away.

In the 21 New Hampshire polls between early July and December 10, Mr. Giuliani slipped below 20% five times, according to polls collated by RealClearPolitics.com. In the 11 polls taken while Mr. Giuliani was advertising heavily, he attracted less than 20% support nine times.

Put another way, between the beginning of July and early November, Mr. Giuliani polled an average of 21% in New Hampshire. In the following four weeks, when he was advertising heavily, support dropped to an average of 18%.

Mr. McCain, meanwhile, has shown a steady increase over the same period, with the RealClearPolitics poll average showing him overtaking the mayor in recent days.

An unnamed “top Giuliani aide” told Politico.com that the retreat from New Hampshire would allow the campaign “to marshal our resources for Florida and February 5, while keeping options open for changes in the early states.”

Mr. Giuliani’s appeal to national voters stemming from his performance in the aftermath of the terrorist attacks of September 11, 2001, has been eroded recently because of nagging doubts about his judgment.

No sooner had his former police chief, Bernard Kerik, been indicted on tax fraud and corruption charges than anomalies were reported over Mr. Giuliani’s security detail as mayor.

It emerged that while courting his third wife, Judith Nathan, in the Hamptons, security was billed to obscure city agencies.