AUGUSTA – Common Cause President Chellie Pingree said Tuesday she plans to leave the Washington-based national watchdog group after four years as its president to “consider political opportunities back in Maine.”

Pingree, a former Democratic state legislator from North Haven who unsuccessfully sought to unseat Republican Sen. Susan Collins in 2002, said she informed her staff of her decision on Monday and intends to step down next month.

Pingree said leaving Common Cause would free her up to explore whether to seek election to the U.S. House of Representatives from Maine’s 1st District.

“This is a great organization to work for,” Pingree said, “but my heart is in Maine.”

The 1st District incumbent, sixth-term Democrat Tom Allen of Portland, has signaled he may run against Collins next year but has not announced he will do so.

In anticipation of such a step by Allen, numerous Maine Democrats have been eyeing what could become an open congressional seat.

On Tuesday, York County District Attorney Mark Lawrence announced formation of an exploratory committee for a possible run for the 1st District seat. Lawrence is a former Maine Senate president who lost a 2000 election for U.S. Senate to incumbent Republican Olympia Snowe.

Earlier this month, Michael Brennan, the former Democratic leader of the state Senate, announced that he was forming an exploratory committee to pursue a 1st District candidacy.

Pingree served in Maine’s state Senate from 1992 to 2000, spending her last four years there as majority leader.

Last June at the Maine Democratic State Convention, Pingree warned a women’s breakfast audience against excessive partisanship even as she expressed hope that national elections in the fall and in 2008 could bring about “a very different country.”

Pingree lauded the federal Justice Department for pursuing evidence of wrongdoing in the “ethics scandal” that had embroiled the nation’s capital and pointed to public financing as a way of refocusing political campaigns.

Saying that as a leader of a nonpartisan citizens’ advocacy group she remained “a liberal and a progressive and a Democrat,” Pingree said concerns over honesty and openness in government can prompt the public to mistrust Democrats and Republicans alike and adopt an attitude of “a pox on both their houses.”

One of Pingree’s children, Hannah Pingree, is majority leader of the Maine House of Representatives.

Allen won the Democratic nomination for Congress in 1996 by defeating state Sen. Dale McCormick in a highly competitive primary and was first elected to the U.S. House with 55 percent of the vote against Republican Rep. James Longley.

He has been re-elected five times since then, most recently defeating Republican Darlene Curley and independent Dexter Kamilewicz.

Collins, who is gearing up to seek a third Senate term, was first elected to the Senate in 1996, defeating Democrat Joe Brennan with 49 percent of the vote. She was re-elected in 2002, winning 59 percent of the vote in her race against Pingree.