In a rematch of a race that was decided by fewer than 3,000 votes two years ago, Rep. Albert Wynn (D-Md.) and community activist Donna Edwards (D) are wooing various interest groups while at the same time attempting to undermine the other’s endorsements.

With just four weeks to go in the 4th district Democratic primary,

outside groups are stepping up their presence in the district and proving why the battle for endorsements in the race has become especially bitter. At this stage there’s a clear distinction between those endorsements that will really make a difference and those that are simply nice additions to a long endorsement list.

“Endorsements have different values at different times in a campaign, and what you need now is … people who are willing to talk to voters and get them out to vote and spend money,” said one Maryland Democratic consultant who did not want to be named.

Last week, two independent expenditures were made for the 4th district race: a $250,000 anti-Wynn television ad buy by the political arm of the national Service Employees International Union and $17,000 for media consulting and pro-Edwards robocalls by the Sierra Club’s political committee.

Edwards’ other key endorsements have come from liberal interest groups like MoveOn.org, EMILY’s List and the National Organization for Woman, which have strong organizations and the financial means to back up their preferred candidates.

For many of the groups that are now supporting her, the 2006 campaign went a long way toward showing that Edwards is a viable candidate against Wynn.

“The SEIU endorsement is important because they don’t just endorse and they don’t just give money — they put together workers and phone banks and canvassers and that kind of muscle and that’s going to very important because she got a lot of steam last time … without a lot of stock campaign resources,” said Ronald Walters, director of the African American Leadership Institute at the University of Maryland and a former campaign strategist for the Rev. Jesse Jackson.

But after winning by just 3 points last time after years of invincibility, Wynn has vowed not to be caught by surprise again. The Congressman has spent a lot of time touting his liberal credentials in Prince George’s County, his majority-black base, and the part of his district that falls in Montgomery County, where Edwards beat him by an almost 3-1 margin.

Wynn has successfully — and not surprisingly — attracted the local development and business community to his corner. He has been close to those business sectors in the past, and Edwards, an attorney, first became known in the community by raising questions about the massive National Harbor development under way in Prince George’s County.

At the same time, Wynn has been aggressively trying to hold on to the labor endorsements that once came so easily for the eight-term Congressman before he was caught by surprise by Edwards’ vigorous challenge in 2006.

“This time I think the labor movement is looking very carefully at its endorsements,” Walters said. “And this time around I think both of them are going to be asking the labor unions to go the next mile. … The ground game is going to be very important.”

One group that could be a key resource for Wynn is the Maryland State Teachers Association, a particularly strong organization that falls under the umbrella of the National Education Association. It’s a group that came out for Wynn not long after he endeared himself to the teachers’ cause when he split with some Democratic leaders during last fall’s reauthorization battle over the No Child Left Behind law. Wynn circulated a well-publicized letter in which he expressed concerns about the law’s continued reliance on standardized tests and proposals to experiment with pay-for- performance programs for educators.

Wayne Clarke, a Democratic consultant and lobbyist in Prince George’s County, called the MSTA a “sleeping giant” in the primary race.

“I think they have the potential to be a very strong force. The question becomes how much resources are they going to pour into it,” Clarke said.

Wynn also has made much of his endorsement by Speaker Nancy Pelosi (D-Calif.) and other Congressional Democratic leaders, but Clarke said he expects local names will be more important to the Congressman in the coming weeks.

“I would anticipate that local elected officials and established elected officials such as state Senators and even county folks with organizations may come out for [Wynn],” Clarke said. “That would help him on the ground, from the grass-roots perspective.”

EMILY’s List could be a great source of last-minute revenue for Edwards. But it also helps Wynn attack his challenger for raising so much money from outside the district. Campaign finance reports show that more than 80 percent of Edwards’ fundraising money comes from outside the district.

EMILY’s List Communications Director Ramona Oliver said that Edwards support from around the nation should be a mark of the strength of her campaign.

“EMILY’s List and its network around the country want to see leaders like Donna Edwards,” Oliver said. “That is the whole nature of EMILY’s List … and that desire for leaders like Donna Edwards does not stop at the district line.”

To counter the argument that she is accepting too much money from out of state, Edwards’ campaign has been quick to point to Wynn’s acceptance of corporate special-interest money, which has been a major source of funding for his campaign. In trying to highlight the issue Edwards went so far last week as to pledge to never accept corporate PAC donations in her campaigns.

With no public polling released on the primary so far, the race must be considered a tossup.

“Coming down to the last few weeks anyone who tells you they are going to win, hang up the phone or walk away,” Clarke said. “I don’t think anyone knows. … I think it’s going to be another long night.”