The frenzied mobilization by both parties and their surrogates in Massachusetts grew even more intense on Tuesday, as Democrats began pouring millions of dollars into the special Senate race to try to stave off disaster and Republicans grew more optimistic about pulling off an upset.

The parties and an array of outside groups have taken to the airwaves, the Internet and the ground in hopes of swaying the final vote next Tuesday in the race between state Attorney General Martha Coakley (D) and state Sen. Scott Brown (R), which has evolved into a national political referendum. Republicans now see a genuine opportunity for an upset — or at the very least the chance to send a message about the national political mood in 2010.

In a fresh sign of increasing nervousness among Democrats about the race, the national party committees on Tuesday chipped in more than $1 million to help boost Coakley’s prospects.

The Democratic National Committee is directing $500,000 in in-kind contributions to the Coakley campaign and the state Democratic Party, while the Democratic Senatorial Campaign Committee has spent more than $500,000 on an ad buy in the Boston and Springfield markets, the first independent expenditure by either national party in the race.

The Massachusetts Democratic Party also launched an ad Tuesday night that specifically targets Brown’s record, a sharp departure from the party’s strategy of essentially ignoring Brown for most of the race.

DNC aides Hari Sevugan and Michael Czin have also been dispatched to Massachusetts to lend a hand in the race’s final days.

Massachusetts Democratic Party Chairman John Walsh told Roll Call that Organizing for America, an arm of the DNC built from President Barack Obama’s 2008 campaign organization, has spread the word to its activists to come help on the ground.

“The call’s gone out that we need all hands on deck, formally, informally … by carrier pigeon, whatever we can get,— Walsh said.

The White House has said Obama does not plan to campaign for Coakley, but even Democrats will privately acknowledge her wide polling advantage has been reduced to single digits.

A Rasmussen Reports poll of likely voters released Tuesday evening showed Coakley ahead by just 2 points, underscoring the erosion in her standing and the potential for an embarrassing upset.

The president, however, has penned a fundraising e-mail for Coakley in recent days, as have Sens. John Kerry (D-Mass.) and Jeanne Shaheen (D-N.H.). In addition, the entire Massachusetts Congressional delegation (all Democrats) headlined a Washington, D.C., fundraiser for Coakley on Capitol Hill on Tuesday night.

Neither the national Republican Party nor the state GOP has aired any ads in the race yet, and the national committees are keeping their homestretch spending plans close to the vest.

However, a number of Republican-leaning independent groups, including the U.S. Chamber of Commerce and several advocacy groups that supported conservative third-party candidate Doug Hoffman in another wild special election in upstate New York this past fall, have swooped in to fill the gap.

The chamber confirmed Tuesday that it had bought “significant— airtime for a positive spot that began airing Tuesday, praising Brown’s record on jobs. The chamber’s ad is the second from an outside group, following a $400,000 ad buy from the American Future Fund criticizing Coakley’s position on taxes. And two other conservative political action committees, the National Republican Trust PAC and Our Country Deserves Better PAC, which is affiliated with the Tea Party Express, have endorsed Brown and plan to run ads on his behalf in the final four or five days, they told Roll Call.

Democrats are seizing on the third-party groups’ involvement to reinforce their argument that Brown is an extremist and far out of the Massachusetts mainstream — a theme that the Coakley campaign and its surrogates have hammered heavily in recent days. In a release, the DNC also said that Brown’s $1.3 million fundraising haul from an online “money bomb— Tuesday came in large part from “the most radical elements of the national Republican Party.—

“I think that because of the timing and the nature of the campaign, voters have not had a chance to really examine Scott’s records and his positions,— the state Democratic Party’s Walsh said, citing Brown’s record on abortion, climate change and national security issues.

Coakley hit this same message in a negative ad, released Monday night, that seeks to paint Brown as a politician operating “in lock step with Washington Republicans.—

The hope is to raise Brown’s low unfavorable ratings while scaring away moderate and Democratic-leaning voters — more than half the Massachusetts electorate is not registered with a party — who may have been attracted to Brown’s outsider message.

Republicans have dismissed the attacks as an attempt to distract voters. One GOP aide close to the Brown campaign said she did not “expect the campaign to go negative— in the final days and instead plans to continue making positive appeals, focusing on issues such as health care and taxes.

Brown will, however, respond to Democrats’ critiques, as he did with an ad on Tuesday that pushes back against the Coakley campaign ad. In his spot he pledges “to take on the political machine and their candidate.—

Third-party groups are also gearing up their involvement in support of Coakley. The Service Employees International Union is spending $685,000 via its Committee on Political Education on a statewide ad buy beginning today.

The Massachusetts AFL-CIO is also rallying its troops, President Robert Haynes said. The union has a voter file of more than 300,000, and Haynes estimated that in total it would send out hundreds of thousands of pieces of mail. “We’re the ground troops,— he said. “All our local unions are doing mail and phone banks and getting out the vote before next week.—

Abortion-rights organizations EMILY’s List and Planned Parenthood are also actively supporting Coakley, though they have yet to report any independent expenditures on her behalf.