Marie C. Johns, a former telecommunications executive and longtime civic activist, launched a campaign for D.C. mayor yesterday, becoming the third candidate to officially enter the race to replace Anthony A. Williams.

A relative unknown who has never held elective office, Johns (D) declared her candidacy before a gaggle of reporters outside the D.C. Office of Campaign Finance, where she filed an official statement of candidacy. Then, under a broiling sun, she knocked on doors in one of the largest precincts in Northeast Washington, the start of a year-long "walking tour" to introduce herself to city voters.

Johns made no speech, and she declined to answer many questions, saying she has yet to work out "really solid policy positions." For now, she said, voters should evaluate her on the basis of "where I've been," saying that her activism and tenure as president of Verizon Washington have prepared her for the mayor's office.

"I'm probably one of the few people you know who's been both a secretary and a CEO," Johns said in an interview. "I come from a solid working-class background. I'm a product of public education. I've been a leader of a major business in this city. I have a long, long list of civic involvement. So I've had the benefit and privilege of knowing the city side to side and top to bottom. That's what I offer."

Johns, 53, was born in Indianapolis and moved to the D.C. area in 1985. After living in Bethesda, she moved to Ward 3 in far Northwest Washington in 1999. Over the past two decades, she has assembled a lengthy civic resume, serving in leadership posts in the D.C. Chamber of Commerce, YMCA Washington, Howard University, the National Capital Revitalization Corp., the Girl Scouts and the Coalition of 100 Black Women.

Beyond that, Johns stressed the importance of improving the city's troubled public school system, expanding early-childhood education and creating a community college so students who aren't bound for four-year colleges can prepare for good-paying trades. She criticized recent proposals to sink hundreds of millions of dollars into crumbling school buildings, saying, "Just throwing money over the transom into a process that's not well thought-out and well designed is not the answer."

Johns said health care, affordable housing, job creation and business development are also "big things I want to talk about." She declined to comment on the city's decision to build a publicly financed baseball stadium -- an issue that has stirred strong emotions -- saying, "That's not really something I'm prepared to get into."

So far in the 2006 race for mayor, Johns faces D.C. Council members Adrian M. Fenty (D-Ward 4) and Vincent B. Orange Sr. (D-Ward 5). Council Chairman Linda W. Cropp (D) and lobbyist Michael A. Brown also are expected to enter the race. Williams has yet to say whether he will seek a third term, but supporters are growing increasingly doubtful that he will run again.

Johns campaign adviser Marshall Brown acknowledged that his candidate faces a field of better-known contenders. But he said she can overcome that disadvantage by making "a lot of contact with a lot of citizens. And that's what we're going to do."

That strategy proved successful for another unknown: Brown's son Kwame, who defeated incumbent Harold Brazil (D) last year for his at-large council seat. Borrowing from Kwame Brown's campaign, Johns planned to wave at rush-hour drivers yesterday afternoon. And she has a full itinerary of door-knocking, handshaking, church-visiting and sign-waving scheduled for weeks to come.

"I've signed my papers," she said. "I'm ready to go."

Marie C. Johns visits with South Dakota Avenue NE resident Bernice Johnson as she begins her door-to-door campaign for mayor in Ward 5.