Democrats continue to dominate Republicans in voter registration in at least eight states expected to be among the most competitive in the November presidential election, an Arizona Republic analysis shows.

In Colorado, for example, Democrats picked up a net 54,000 registered voters from April to August. Republicans added a net 11,000 in the same period, state records show. Republicans still hold a narrow lead over Democrats in registered voters in that state.

Pennsylvania added 107,000 registered Democrats from April to early September, while Republicans added 2,700. Democrats already led registration there.

Fifteen states are considered key battlegrounds in the race for the White House. Six states don't track the party affiliation of voters and another, West Virginia, hasn't updated its figures since spring.

The registration trends are a continuation of a pattern that played out for Democrats throughout the primary season. The surge of newly minted voters favors Barack Obama, the Democratic nominee, but only if he is able to do what few presidential candidates have done: get these new, often younger, voters to the polls in November. John McCain, the Republican nominee, figures to draw from a smaller but more reliable pool of supporters, experts say.

Still, the registration trend suggests Democrats are better positioned for the election in those states.

"The Republicans would love to have those numbers working in their favor," said Thomas Patterson, a government professor at Harvard University. "This is motivated registration. . . . This is, no doubt, a net plus for Democrats."

"That's a precursor to turnout (in November). That's good news for Democrats," said Henry Brady, a political-science professor at the University of California-Berkeley.

He said turnout in battleground states has been higher among newly registered voters than it is in less politically competitive states. Both parties should expect at least 40 percent of the new registrants to show up in November, Brady said.

Among existing registrants, elections officials expect turnout higher than that.

Kenneth Bickers, a political-science professor at the University of Colorado, said the registration figures in his state suggest, but hardly guarantee, that Obama could be competitive there.

"The profile of a McCain voter is someone who is likely to vote no matter what," Bickers said.

Historically, enthusiasm fades among many who register as Democrats, Bickers said, and GOP voters turn out more reliably. Obama successfully marshaled young voters during the Democratic primaries, but many states held caucuses, a format that typically draws only a fraction of voters. His performance there showed organizational strength but not necessarily broad appeal to voters.

Still, the registration trend is in line with the fundraising patterns playing out across the country in the presidential and congressional races. Together, they underscore the reason Democrats think the party could strengthen its control in both the House and Senate and win the White House.

Most states saw a spike in voters registering as independents, and some, including Nevada and North Carolina, registered more independents than Republicans in recent months.

Democrats already had a registered-voter advantage this year in six of the eight battleground states that register voters by party. But four years ago, President Bush won six of these eight states to clinch a second term.

Other likely swing states, such as Michigan and Wisconsin, don't register voters by party.

Ohio allows voters to change party affiliation at will, making it difficult to gauge where voter loyalties lie. The Columbus Dispatch, however, reported that Ohio has added 1 million registered Democrats since 2004, while Republicans added 356,000 voters in that time.

Polling and recent voting history suggest that voters in at least some states, like Florida and North Carolina, may register as Democrats but vote for Republicans in November.

In Florida, Democrats gained 258,000 potential voters from December to July, while the GOP added 101,000. Democrats had a 300,000-voter advantage before the changes.

In November 2004, Democrats had 369,000 more registered voters than Republicans did, yet the state voted for Bush by 381,000 votes.

In North Carolina, Democrats have picked up a net 50,000 registered voters over the GOP since May. They dominate overall registration by about 750,000 voters. But in 2004, with a similar edge, the state still voted for Bush by 400,000.

Polls indicate McCain is ahead in both those states.

In New Hampshire, Democrats netted 4,400 additional voters from January to August, while Republicans lost 3,100.

In New Mexico, Democrats gained a net 13,000 voters over Republicans and hold a commanding 200,000-voter advantage. Still, recent polling suggests the state could be as tight as the past two elections: It went for Al Gore in 2000 and Bush in 2004.

Democrats also added to their existing registration leads in Iowa and Nevada. These states, however, had slim Republican majorities among registered voters four years ago.

Republicans have nearly lost their lead among registered voters in New Hampshire and have a narrow lead in Colorado, though independents are now the state's largest bloc.

The registration figures for half the swing states were tallied before McCain named Alaska Gov. Sarah Palin as his running mate. She is already cited as stirring conservatives, which could alter registration patterns in the closing weeks.