Presidential hopeful Newt Gingrich may be leading in polls of Republican voters in Virginia, but his name won't appear on the state's primary ballot, a significant setback for a candidate whose standing in polls has recently been slipping.

The state party said early Saturday that Gingrich and Texas Gov. Rick Perry had failed to submit the required 10,000 signatures to appear on the March 6 ballot.

Failing to get on the ballot in Virginia, where Gingrich lives, underscores the difficulty first-time national candidates have in preparing for the long haul of a presidential campaign.

And it illustrates the organizational advantage held by Mitt Romney, the former Massachusetts governor, who has essentially been running for president for five years. Romney's team, larger than those of most of his opponents, has paid close attention to filing requirements in each state. He will appear on the Virginia ballot along with Texas Rep. Ron Paul, who also has run a national campaign before.

Ironically, Gingrich had a slight lead over Romney in a Quinnipiac poll of Virginia Republicans released earlier in the week.

The former House speaker surged in popularity in early December and tried to use that momentum to make up for a slow start in setting up a campaign organization and lacklustre fundraising. But his standing in polls has slipped in recent days amid a barrage of negative ads in Iowa, where the Jan. 3 caucuses begin the contest for the Republican presidential nomination.

Gingrich's campaign attacked Virginia's primary system on Saturday, saying that "only a failed system" would disqualify Gingrich and other candidates and vowing to run a write-in campaign.

"Voters deserve the right to vote for any top contender, especially leading candidates," Gingrich campaign director Michael Krull said in a statement. "We will work with the Republican Party of Virginia to pursue an aggressive write-in campaign to make sure that all the voters of Virginia are able to vote for the candidate of their choice."

However, according to state law, "No write-in shall be permitted on ballots in primary elections."

"Virginia code prohibits write-ins in primaries. He can't do it," said Carl Tobias, a law professor at University of Richmond.

Tobias said Gingrich may have had trouble meeting a requirement that the 10,000 signatures must include at least 400 signatures from each of Virginia's 11 congressional districts.

Gingrich's campaign did not immediately respond to a request for comment. Gingrich had been concerned enough to deliver his signatures personally. Rushing Wednesday from New Hampshire, which holds its primary on Jan. 10, he had supporters sign petitions before entering a rally in Arlington, Virginia.

Virginia Republican Party spokesman Garren Shipley said in a statement that volunteers spent Friday validating signatures on petitions that Romney, Paul, Perry and Gingrich had submitted. "After verification, RPV has determined that Newt Gingrich did not submit required 10k signatures and has not qualified for the VA primary," the party announced early Saturday on its Twitter feed. Shipley did not respond to telephone calls Saturday seeking comment.

Forty-six delegates will be at stake in Virginia's primary on March 6, or Super Tuesday, when 11 states are tentatively scheduled to hold Republican nominating contests. That's a small fraction of the 1,144 delegates needed to win the nomination. But they could prove pivotal in a close race, especially for a candidate like Gingrich, who represented a Georgia district in the House and expects to do well in contests in southern states.

In another development, Virginia's Democrats said President Barack Obama's re-election campaign gathered enough signatures to get him on the state's primary ballot though he was the only candidate who qualified.

Three other Republican candidates — Minnesota Rep. Michele Bachmann, former Pennsylvania senator Rick Santorum and former Utah governor Jon Huntsman — did not submit petitions with signatures before Virginia's deadline of 5 p.m. Thursday.

Bachmann and Santorum are pinning their hopes for remaining in the race on strong showings in Iowa where they are battling for the support of social conservatives who dominate the Republican caucuses. Huntsman has focused on New Hampshire.

In Iowa, Perry, Bachmann and Santorum are doggedly, if not desperately, travelling the state in their individual quests for late-game surges in the Republican presidential race.

Running behind in the polls ahead of the caucuses, this trio of conservatives campaigned the old-fashioned way, in town squares, coffee shops and community centres. But time is short for them to rise. And, for Bachmann and Santorum at least, money is, too.

Bachmann and Perry each logged more than 1,600 kilometres last week aboard campaign buses that made stops at gas stations and catering companies, sports bars and churches. Santorum, who visited each of the state's 99 counties on his own tour earlier this year, is spending the run-up to the caucuses returning to many of those places.

The three — their presidential candidacies likely come down to strong finishes in Iowa — are betting that Republicans here will reward them for engaging in the hand-to-hand, retail campaigning that Iowans typically demand of White House hopefuls. The leading contenders in polls — Romney, Gingrich and Paul — have simply popped into the state on occasion to woo voters rather than planting themselves in the state.

To varying degrees, Romney, Gingrich and Paul have chosen to compete primarily through TV advertising, nationally televised debates and interviews on media outlets such as Fox News Channel. And that strategy has seemed to pay off for them: They are clustered at the top of the Republican field, at least for now.