There were immediate calls for the married father of three's resignation on Monday, after he was accused of beginning Valentine's Day with a high-class call girl.

At a news conference with his wife, the 48-year-old apologised to his family and the people of New York, saying: 'I have disappointed and failed to live up to the standard I expected of myself.'

But the man once tipped as a possible Democratic presidential candidate, who staked his reputation as an 'Untouchable' on his hard-headed integrity, did not discuss his political future.

The news was met with disbelief even in Albany, a state capital accustomed to scandal. 'We're at a total standstill,' said Harlem Democratic assemblyman Keith Wright. 'Everybody is absolutely stunned.'

Mr Spitzer is also a Democratic superdelegate who pledged to support Mrs Hillary Clinton's bid for the White House at the party's convention in August. She sidestepped questions about the sex scandal and its possible effects on her campaign.

The man who made extensive use of electronic surveillance during his time as state attorney-general is believed to have been caught on a federal wiretap arranging a Feb 13 meeting in a Washington hotel room with a prostitute from the Emperors Club VIP.

An affidavit based on the wiretap told of a man identified as 'Client 9' paying out US$4,300 (S$6,000) in cash, some of it as credit for future trysts, some of it for sex with Kristen, a 'petite, pretty brunette'. He was also described as a 'difficult customer' with an agency reputation for requesting services 'you might not think were safe'.

The governor has not been charged and prosecutors would not comment, but a law enforcement official said that any charges would probably focus not on the fact that he had hired a prostitute, but how he paid for it.

If payments were made in such a way as to conceal their purpose and source, he could be charged with 'structuring', a crime carrying a penalty of up to five years in prison. As he allegedly paid Kristen's train fare from New York, he could also be charged with transporting prostitutes across state lines.

The scandal comes 16 months after Mr Spitzer stormed into the governor's office with a historic margin of victory. But his first year was marred by turmoil, including an unpopular plan to give illegal immigrants driver's licences and a plot by his aides to smear a Republican enemy.

As the latest scandal broke, Long Island Republican congressman Peter King said: 'He has to step down.'

As attorney-general, Mr Spitzer had prosecuted at least two prostitution rings.

Mr King said: 'I never try to take advantage or gloat over a personal tragedy. However, this is different. This is a guy who is so self-righteous and so unforgiving.'

But there was gloating on Wall Street, where Mr Spitzer had uncovered corruption with moral fervour, earning himself the nickname 'Sheriff of Wall Street' and Time's 'Crusader of the Year' award.

Mr Chuck Gabriel, head of Capital Alpha Partners, said of his apparent downfall: 'People are somewhat gleeful... This is a guy who had Wall Street under his thumb, and now he's fallen into the same kind of trap as those who suffered under his hand.'

ASSOCIATED PRESS, NEW YORK TIMES, LOS ANGELES TIMES, REUTERS