Republican Patrick Meehan, a former U.S. attorney, announced Monday that he is running for Pennsylvania’s open 7th Congressional District seat — a move that makes a highly competitive race in 2010 more likely.

As a result, CQ Politics has changed the rating on that race to “Leans Democratic” — which means the seat is definitely in play — from the mildly competitive “Democrat Favored” category.

By making his widely expected candidacy official, Meehan gives Republican strategists the top-tier candidate they’ve sought for the contest to succeed two-term Democrat Joe Sestak in the suburban Philadelphia district. Sestak has entered the Democratic Senate primary to challenge five-term incumbent Arlen Specter , who in April switched from the Republican Party.

Meehan, a former federal prosecutor and county district attorney, said in his prepared remarks that he is running for the House in response to local voters’ dissatifaction with the federal government.

“I have looked the citizens of this Commonwealth in the eye as they have shared with me their deepest fears and their greatest hopes,” Meehan said, referring to the state’s formal name as the Commonwealth of Pennsylvania.

“They have told me they feel as if their voice just isn’t being heard in Washington, that the representatives they have elected have sold them out to the special interests, that government now seems to be something that is imposed on them, rather than something that is working for them,” Meehan said.

Meehan previously dropped plans to enter the 2010 Republican primary for governor.

To clear the path, Steven Welch, a Republican businessman who had announced plans to run in the 7th, said Saturday that he would instead run in the adjacent 6th District. That seat also is open, because four-term Republican Jim Gerlach is running for governor next year.

While the open 7th District seat will require a strong defensive effort by the incumbent Democrats, they will not be short of politically experienced contenders. State Rep. Bryan Lentz is a confirmed candidate, and state Rep. Greg Vitali is considering the race.

Meehan will be seeking to restore a longtime Republican hold on the district that was broken in 2006, when 10-term GOP Rep. Curt Weldon was unseated by Sestak. But Meehan, to win, will have to reverse a Democratic trend in a district that gave 56 percent of its votes to Barack Obama for president in 2008, the same year in which Sestak won a second term with 60 percent.

Pennsylvania’s 7th draws more than 70 percent of its voters from Delaware County, which abuts Philadelphia to the southwest and which the 7th shares with the Philadelphia-based 1st District. The 7th District also takes in parts of Chester and Montgomery counties.

Delaware County last voted Republican for president in 1988, when George Bush took 60 percent of the county vote en route while winning 51 percent of the statewide vote. In 2008, the county gave 60 percent to Obama, who extended the Democrats’ statewide presidential winning streak in Pennsylvania to five elections.

Meehan was elected district attorney in Delaware County in 1995 and re-elected in 1999. He then was tapped in 2001 by President George W. Bush to become U.S. Attorney for the Eastern District of Pennsylvania.