FAIRFAX, Va.— Thousands of Republican volunteers braved scorching temperatures to knock on doors and canvass voters on Saturday as the party staged its first “Super Saturday” blitz hoping to energize supporters and rival Democrats’ volunteer mobilization.

Republican party officials said volunteers were out in a dozen battleground states expected to see close contests in the Nov. 6 election between Democratic President Barack Obama and his Republican challenger, former Massachusetts governor Mitt Romney.

Obama captured all 12 — Virginia, North Carolina, Florida, Ohio, Pennsylvania, Michigan, Wisconsin, New Hampshire, New Mexico, Colorado, Nevada and Iowa — when he won the White House in 2008, aided by armies of enthusiastic supporters who helped generate the highest voter turnout in 40 years.

Romney will need to swing a number of them back to the Republican column to defeat Obama this year. Drumming up voter enthusiasm could be a key, especially given polls showing Democrats are more enthusiastic about the 2012 contest than Republicans.

“There’s nothing to substitute for face-to-face, eye-to-eye contact,” former Virginia Governor George Allen told volunteers in Fairfax.

Allen, also a former U.S. senator, is in a tight race against another former Virginia governor — and close Obama ally — Tim Kaine, to win back his old Senate seat.

A CNN poll this week said 59 percent of registered voters nationwide who describe themselves as Democrats are extremely or very enthusiastic about voting, up from 46 percent in March.

Fifty-one percent of registered voters who say they are Republicans are extremely or very enthusiastic about voting, unchanged since the earlier poll.

A Pew poll released this week found 60 percent of Republicans find the presidential campaign dull, compared with 46 percent of Democrats. But Romney raised more funds than Obama in May and is likely to be ahead of him in June when he pulled in more than $100 million.

Obama’s campaign is mounting a massive volunteer organization again this year, after reactivating its 2008 network and creating a heavy presence in social media.

In Virginia, Democrats have been holding voter registration drives as often as several times a week, and making telephone calls and knocking on doors in weekend events for months.

But Republican officials said they were determined to catch up with an intense ground game of their own. The party and Romney’s campaign have opened 23 offices in the state in the hope of recapturing Virginia’s 13 electoral votes this year.

“No matter how much the president decides to stick into the state, we’re going to match them,” one party official said.

In Fairfax, about 120 Republicans came out in 106-degree F (41-degree C) heat on Saturday to knock on voters’ doors. Dozens staffed a telephone bank.

Jane Pyrak, 51, a stay-at-home mother of three from Annandale, said she volunteered twice a week and expected to do even more as the election came closer.

A lifelong Republican, she said she became part of the fiscally conservative Tea Party movement because she opposed Obama’s economic stimulus and healthcare reform plans. She said she also opposes Obama’s support for abortion rights.

“This is the most active I’ve been in my life,” Pyrak said. “It’s very exciting.”

Republican officials said they did not have an estimate of how many people had participated in “Super Saturday” nationwide, but were sure it was in the thousands.

They plan to hold similar events once a month until the election, to contact voters and collect data they can use to make decisions such as where to deploy volunteers or focus voter turnout efforts during the last weeks of the campaign.

Obama became the first Democratic presidential candidate in 44 years to win in Virginia four years ago, but Republicans have dominated elections in the state in each of the three years since.