Ask not whether you have the desire, the resources, and the stamina to be a Congressional candidate in Massachusetts; ask whether a Kennedy is in the race.

Democratic Rep. Barney Frank’s announcement that he would not run for re-election in 2012 opened the door for a bevy of ambitious candidates eyeing the state’s 4th district, a safe Democratic seat. But one contender has the potential to change the fundamental dynamics of the race. Until Joseph Kennedy III, who has said he is considering a run, makes a final decision, the field will remain in a deep state of flux.

If Kennedy, the 31-year-old attorney son of former Rep. Joe Kennedy (D-Mass.) and the grandson of Robert F. Kennedy, jumps in the race, other candidates may decide to wait for another shot at Congress.

“He has the ability to do what Elizabeth Warren did, which is to basically clear the field,” Massachusetts Democratic strategist Mary Anne Marsh said, referring to the presumptive Democratic nominee for Senate.

Jesse Mermell, a selectwoman in the city of Brookline who is seriously looking at a Congressional run, said there were myriad considerations. Speaking to Roll Call as she drove around the district, Mermell said she had been on the phone since Frank announced his retirement, feeling out the potential for fundraising, ground organization and the political climate.

As for the specter of Kennedy jumping in, she said, “Anyone who tells you it’s not part of their decision-making process is lying.”

Fall River Mayor William Flanagan, who has left the door open to a bid for the seat, said if Kennedy entered the race it would change the dynamic of the field. “He does bring in name recognition, and he would have the ability to raise finances given his connection to his family and his family’s connection to the Democratic Party,” he said.

But Flanagan, Mermell and other potential entrants in the race all told Roll Call their final decision would be based on factors besides Kennedy.

“We are a commonwealth with great political bench strength,” Mermell said. “So whatever this field looks like, it’ll be strong.”

Other possible Democratic contenders include state Sen. Cindy Creem, former Brookline Board of Selectmen Chairwoman Deborah Goldberg, City Year co-founder Alan Khazei, who recently dropped his bid for Senate, Bristol County District Attorney Samuel Sutter and state Sen. Marc Pacheco.

Regardless of who runs, geography will play an outsize role in the race. The 4th district meanders from the deeply liberal cities of Brookline and Newton to part of the conservative but Democratic blue-collar city of Fall River. The 34 municipalities in the district range from Brookline, which voted 81 percent for Barack Obama in 2008, to Wrentham, the home of Sen. Scott Brown (R), which gave him 73 percent of the vote in the 2010 special election.

Given the vastly different communities in the 4th, the open-seat race is almost certain to draw candidates with a base of support in one part of the district but not in any other parts. Without Kennedy, that is likely to mean a Democratic primary with many candidates. And it wouldn’t be unprecedented in Bay State politics. In the 1998 primary to replace the retiring Joe Kennedy in the 8th district, 10 Democrats battled for the nomination.

The then-mayor of Somerville, Mike Capuano, managed to win that race with old-fashioned shoe-leather politics. Capuano, now in his seventh term, said in an interview that the heart of his success was “door-knocking and street work.”

“I had the least amount of money of any of the major candidates by far, but I had a great organization,” he said. “Campaigns are much better done with direct voter contact: person to person. Enhanced, obviously, by a good ad, if you can afford to put an ad up, or a good Web presence, good email, all that other stuff. But it really has to be [that] the backbone is personal interaction.”

One poll taken during the 1998 race found almost half of Capuano supporters had met him.

In a parallel to what the 4th district race might look like, Capuano had a strong base of support in his hometown and won Somerville, but he managed to win the election by coming in second place in every other municipality.

To avoid conflicting with Jewish holidays, next year’s Bay State primary is scheduled for Sept. 6, a Thursday. That bodes for a low-turnout affair in which a strong ground game will be key.

Even for a Kennedy.

“It’s a mistake to think that the Kennedy name is a magic elixir,” Capuano said. “It is a great beginning, and I know this particular kid, and he’s a good, capable kid.”

But, Capuano said, if Kennedy gets in, “even he will have to do the grunt work. I guarantee that.”