The woman at the head of the company, Ms. Palfrey, contends that it was a legitimate escort service before being shut down last year. Federal prosecutors say it was a prostitution ring, and a State Department official, Randall L. Tobias, resigned in April with the disclosure that he had been a client.  But Mr. Vitter is the first member of Congress to admit an association. Hustler magazine said Tuesday that it had uncovered that link and that the senator’s public admission had resulted from its subsequent call to his office.  In New Orleans, meanwhile, the madam of a high-priced brothel that was shut down by federal authorities in 2002 told a local television station, WDSU, that Mr. Vitter was one of her clients in the 1990s. The woman, Jeanette Maier, called him “one of the nicest and most honorable men I’ve ever met.” Mr. Vitter’s office did not immediately return a call for comment Tuesday night.  Mr. Giuliani said Tuesday after a town-hall-style meeting in Concord, N.H., that he had not spoken to Mr. Vitter and that there had been no decision about whether the senator would remain in the campaign.  “I believe that this is a personal issue,” Mr. Giuliani said. “We are going to have to hear from Senator Vitter. I think you look at all the people I appointed — a thousand or so — sure, some of them had issues, some of them had problems. The vast majority of them were outstanding people.”  But Mr. Vitter’s position in the campaign could now be all the more tenuous given the questions surrounding some of Mr. Giuliani’s other choices, including that of Thomas Ravenel, who stepped down as South Carolina campaign chairman last month after being charged with distribution of cocaine.  At home, any fall for Mr. Vitter could be long and hard. A Harvard graduate and Rhodes scholar, he rose from a headline-grabbing stint as a reformist state legislator in the 1990s through five years in the United States House, where he took the seat of Representative Robert L. Livingston, the speaker-in-waiting who resigned in 1999 as a result of a sex scandal. In 2004 Mr. Vitter won a decisive victory in a run for the Senate, a triumph that gave him a position at the top of the Louisiana Republican Party.  Through it all, Mr. Vitter’s consistent themes have been family values, morality and ethics — his own, in contrast to what he has depicted as deficiencies in the local political culture. In Louisiana, where the well-documented infidelities of the onetime governor Edwin W. Edwards were all but a political asset, Mr. Vitter could easily survive any disclosure about adultery. Insincerity, however, is another matter.  “What makes this tougher for him is, one of his stronger campaign messages is a family-values message,” said Wayne Parent, a political scientist at Louisiana State University. “Whatever this is, it addresses the sorts of things he makes the centerpiece of his political message.”  Roy Fletcher, a Baton Rouge political consultant, said: “He’s got very turbulent waters ahead. This thing ain’t going away.”  Five years ago Mr. Vitter was linked by a New Orleans weekly to a prostitute in the French Quarter, an association he angrily denied. But by then his position as a self-proclaimed scourge of lax ethics was well established. In the early 1990s, he quickly established himself as a champion of political morality in the Legislature, taking on Governor Edwards and his associates, firing off ethics complaints, battling casinos and pressing for term limits that this year finally ousted the largely Democratic legislative old guard.  Mr. Vitter’s long shadow is still resented by some of his former colleagues in the Legislature. “He had the feeling that the overwhelming majority of Louisiana elected officials were not straight as an arrow and he was the straightest arrow in the bunch,” said a veteran Democratic legislator, Warren Triche, one of those who left office this year. “He more or less thought he was the best thing to hit the legislative floor.”  Marc Santora contributed reporting from Concord, N.H.  A version of this article appears in print on , on Page A11 of the New York edition with the headline: A Senator’s Moral High Ground Gets a Little Shaky. Order Reprints| Today's Paper|Subscribe
Senator David Vitter of Louisiana, whose phone number was on a client list kept by the so-called D.C. Madam, had depicted himself as a champion of family values.