Nicknamed the "Sex in the City voters", single women are less likely to turn up to the polls than married women but more likely to vote Democrat if they do: a potentially rich source of votes if the Democrats can tap their concerns.

Previously the party's pollsters concentrated on the gap between men, who tend to vote Republican, and women, who are more likely to vote Democrat. But further examination shows that there is a greater difference between married and single women than between men and women.

George Bush has a one percentage point lead among married women in 2000, while single women went for the Democrat Al Gore by 31%.

The trouble is that while 62% of married women went to the polls in 2000, only 43% of singles did. Given how tight the race was three years ago, urging more singles to get to the ballot box will be a crucial issue for the Democrats.

"This split has always existed," said Kellyanne Conway, president of WomenTrend, an organisation which tracks women's attitudes and political concerns.

"What makes it so important now is the growth in the group we are talking about. The number of unmarried women in their 20s has doubled in the last 20 years. Those in their 30s have trebled."

"Single people are overwhelmingly ignored," Bella DePaulo, who studies singles' behaviour at the University of California at Santa Barbara, told the New York Daily News.

"They aren't considered a voting bloc, and no one panders to them. As of 2002, there were 86m single people - 40% of the adult population.

"They are subsidising everybody else, and single people also pay more for almost everything. Politicians should pay attention."

Few, however, have identified them as a group worth addressing, and once they did they would have to find a new political language to attract their attention.

"Single women feel that nobody is speaking to them," Ms Conway said. "They haven't got children in public schools or retirement savings plans, and so they have a less vested interest in the system."

Wooing women voters has long been crucial to the election fortunes of presidential candidates, even though neither party has ever run a woman for president and the Democrats have only once nominated a woman for vice-president - Geraldine Ferraro in 1984.

But the women's vote has proved increasingly unpredictable. Bill Clinton owed his re-election in the 90s in no small measure to the "soccer moms", working women with children concerned about public schools and job security.

Increasingly, however, they have been losing out to the "security moms", who have looked to government to protect their families from terrorist threats.

In the past four months support for Mr Bush among women has slumped by 11%, according to a poll released earlier this week, taking him from 14 points ahead to seven points behind.

But another poll in June showed that mothers were far more convinced that Mr Bush was handling the terrorist threat than non-mothers, and that they were even more worried about national security than men.

Meanwhile, with greater economic independence and more opportunities for career advancement, single women have married social concerns like abortion and crime to economic matters like pay and tax, according to pollsters. This still makes them far more likely to vote Democrat.

"Sex in the City voters are looking for some of the security they are missing in their daily lives," Ms Conway said.

"They're not just concerned with military security, but kitchen table economic security and social security. The government is a partner or safety net when you are going it alone. For women without husbands, Uncle Sam and Big brother are their greatest protectors."

Once they get married and have children, however, things begin to change. "It's all about the four Ms," Ms Conway said. "Marriage, munchkins, mortgages and mutual funds. Once they have those they become a little bit more conservative and start to tilt towards the Republicans."