Pennsylvania Sen. Arlen Specter’s decision to switch political parties and run for re-election as a Democrat in 2010 reverberated down K Street on Tuesday as lobbyists braced for a dramatically new environment around some of the year’s most heavily lobbied issues.

The move, coming on the eve of President Barack Obama’s first 100 days in office, brings Democrats within one seat of the 60 needed for filibuster-proof control of the chamber.

“The reality is Democrats are going to have 60 votes,— said Steve Elmendorf of Elmendorf Strategies, noting Minnesota Democrat Al Franken’s 312-vote lead over former GOP Sen. Norm Coleman. (A court ruled Franken the winner, but lawyers for Coleman have appealed the ruling.)

“I think the business community is going to have to get very focused on the fact that Democrats are in charge and they have a filibuster [-proof] majority and they should try to work with them more to get things done,— he added.

Specter’s switch has implications across a broad swath of policy areas as the Obama administration tees up massive governmental reforms on health care, climate change, labor and economic policy.

Specter, who previously chaired the Senate Judiciary Committee, also could provide Democrats with a much-needed vote on a Supreme Court justice pick in the near future.

Republicans downtown reacted with shock and dismay over Specter’s decision.

“As a longtime Republican going back to the Reagan administration, I’m really unhappy we forced him out of the party,— said Steven Hart of Williams & Jensen.

Other K Street Republicans said Democrats now have the chore of trying to keep Specter in line.

“I don’t think this makes any difference on how Specter is going to vote,— said Jade West of the National Association of Wholesaler-Distributors. “Specter has voted as a maverick for his entire career.—

However, Specter’s party switch could mean more to Republican lobbyists’ bottom lines than they’d like to admit.

After largely maintaining their grip on K Street by tapping into business’ desire to block potentially harmful legislation, Republican lobbyists may see their star dim as moderate Democrats such as Sens. Tom Carper (Del.), Blanche Lincoln (Ark.), Ben Nelson (Neb.) and Mark Pryor (Ark.) become the key bloc deciding whether major legislation advances.

“K Street is still dominated by Republicans and now there is no reason whatsoever to hire them in the current environment,— one Democratic lobbyist said.

Republican lobbyists were quick to note that Specter’s party switch doesn’t necessarily change the equation on major legislation such as the Employee Free Choice Act.

Specter said in a statement that he would still vote against the “card check— bill, and business groups regard that as a significant win.

Unions see Specter’s shift as a new opportunity to try to sway the Pennsylvanian on card check.

Word of Specter’s party switch came as Service Employees International Union members protested at a downtown D.C. Bank of America branch.

The union, which is demanding that the bank’s CEO Ken Lewis resign, hosted a series of protests around the U.S. on Tuesday.

Stephen Lerner, an SEIU official participating in Tuesday’s event, said Specter’s defection is proof that “there’s a growing feeling in the country that Republicans are not part of the solution.—

“It’s always good news to see the majority party become an even bigger majority party,— he said.

Later Tuesday afternoon, another union official said privately that Specter’s move “changes the environment significantly— for organized labor’s agenda, noting that “the labor community has a long history with Arlen Specter.—

In the previous Congress, Specter supported an ill-fated card-check bill that would have made it easier for workers to join a union.

The Senator has since had a change of heart, however, officially changing his tune last month after prominent conservative activist and former GOP Rep. Pat Toomey began exploring a primary challenge.

“He’s more freed up to vote his conscience,— the labor official said.

“He’s been in a difficult position lately, having to make decisions based on short-term political calculus rather than what’s genuinely in his heart,— the official added.

Former Rep. David Bonior (D-Mich.), chairman of the union-backed American Rights at Work coalition, noted Specter’s long history of supporting unions, saying in a statement that “we look forward to working with Senator Specter to continue the fight for progressive reforms for working families.—

Additionally, Specter’s party switch could create more opportunity for unions on labor policy that he’s supported in the past like the Family and Medical Leave Act, mandatory health care benefits, and increased minimum wage.

Legislation to deal with greenhouse gas emissions may also have a better chance in the Senate.

“It puts climate change legislation in the realm of possibility,— said one environmental group lobbyist.

Matthew Murray contributed to this article.