After more than three decades as the standard-bearer for Montgomery County's Democrats, Joseph M. Hoeffel III chose Monday to put down the flag. The county commissioner said he would not seek reelection this year, succumbing to weeks of party pressure.

He threw his support behind rising Democratic star State Rep. Joshua Shapiro, a former aide to Hoeffel who announced his own bid for the commissioner's job moments after his former boss stepped aside.

Shapiro and running mate Leslie Richards, a Whitemarsh Township supervisor, are poised to receive their party's nomination later this month and dramatically reshape the campaign as their party seeks to wrest control of Montgomery County government from the Republicans for the first time in decades.

"I really do feel liberated," Hoeffel, 60, said at a joint news conference with Shapiro. "I've run for office 16 times. That's more than enough for any sane man."

For his part, Shapiro vowed to follow Hoeffel's lead, emphasizing economic development and job growth in this year's campaign.

"We know we have big shoes to fill," he said. "But we wear our own shoes, and we're going to use them to walk in new directions and blaze new trails."

Monday's maneuvering ended months of speculation that arose after local Democratic leaders first floated the idea of replacing Hoeffel with Shapiro on their 2011 ticket. Pressure for Hoeffel to step aside began building in December, when local Democratic Chairman Marcel Groen said he would not support his reelection bid.

Groen questioned Hoeffel's viability as a candidate after a failed campaign in the Democratic gubernatorial primary last year and a contentious three years at the helm of county government that resulted from a power-sharing deal with his Republican colleague on the board, James R. Matthews.

The controversial bipartisan arrangement, announced days after the 2007 election, strained relations for both men within their parties and with odd-man-out Republican Commissioner Bruce L. Castor - so much so that Montgomery County government has been known more for its squabbling in recent years than for any policy initiatives.

It didn't help that Montgomery County District Attorney Risa Vetri Ferman announced in the waning days of 2010 that a grand jury was investigating allegations that Hoeffel and Matthews violated state open meetings laws by discussing government business over regular breakfast meetings. Matthews announced last month that he would not seek reelection.

"It became clear to me that the best thing for everyone involved was to have a united party," Hoeffel said.

It was an abrupt about-face for a man who has become known for his perpetual candidacy during the last 37 years. The son of an Abington surgeon, Hoeffel entered Montgomery County's Republican-dominated political scene with a failed bid for the state House in 1974. But within years, he became known as the one Democrat who could not be beaten at county polls, winning a series of elections for that seat and later the county's Board of Commissioners and a seat in the U.S. House, which he held for six years.

Lately, his political light has dimmed, with two recent failed campaigns for statewide office, the last being the gubernatorial bid in which Hoeffel placed fourth among four Democratic candidates, even in his home county. He said Monday that after finishing his term, he will field teaching offers at area universities and continue to shop around a nonfiction book on politics.

To many party insiders, Shapiro - a fresh-faced 37-year-old father of four, the latest born just last week - has much the same political glow that graced Hoeffel in his early days.

An Abington resident, a Ballard Spahr lawyer, and a chief of staff to Hoeffel during his time in Congress, Shapiro enters the race as a well-regarded four-term legislator with a $1 million campaign fund and no link to the troubles that have plagued Montgomery County government during the last three years. Representing the 153d District, which includes Upper Dublin and Abington Townships, he has made a name for himself sponsoring several high-profile bills and by helping broker a deal in 2007 that elevated Rep. Dennis M. O'Brien (R., Philadelphia) to House speaker and put him in the deputy post.

But with Republicans resurgent in Harrisburg, that influence would almost certainly be diminished this year. The chance to become commissioners' chairman in one of Pennsylvania's wealthiest and most populous counties proved an attractive lure when Democratic leaders first approached him about a bid late last year. He said then, however, he would run only with Hoeffel out of the race, party insiders said.

He plans to hold his post in the state House through this year's county election.

"I feel like I've accomplished a lot in Harrisburg," he said. "But I look forward to addressing the challenges closer to home in Montgomery County."