Will he ... or won't he?

The evidence points to the conclusion that Mayor Thomas M. Menino will run for an unprecedented fifth term. But today, even as mayoral candidates have their first opportunity to pull nominating papers and begin gathering signatures from city voters, Menino insists that, no, no, he's not running, at least not yet.

"I'm making calculations about my future and the city's future," he said. "It's not being coy."

Menino has often been reluctant to enter the political fray in election years, going to lengths to avoid face-to-face debates and descend into the give-and-take of campaigns. This year, however, the will-he-or-won't-he questions surrounding the mayor's candidacy have become increasingly futile, as Menino casually dismisses all the mounting signs of a full-scale reelection effort.

On March 1, for example, Menino hired a young political operative, Emily Nowlin, a native of De Leon, Texas and a recent graduate of Texas Tech University who was regional director of the Edwards campaign in Keene, N.H., according to her hometown paper, the De Leon Free Press. She is being paid $2,145 every two weeks and was at the mayor's headquarters near City Hall yesterday. She introduced herself to a reporter as the campaign manager but declined to answer questions.

Her boss was not giving up much, either.

"She's a very sharp woman who is in town to help me make my decisions about what we should do about the future," Menino said. "She's working right now to give me indications of the issues that face our city and how we can work through some of those issues."

Menino rented the headquarters at 2 Center Place, across from City Hall, in February. Since then, it has grown into a bustling political office. A handful of volunteers were there yesterday, stuffing manila envelopes and chatting. So were Nowlin and Daniel F. Cence, a seasoned political consultant who is helping to guide Menino's operation. Green signs on the walls proclaimed: "For Mayor Menino." But no one was answering questions.

On Monday morning, the mayor was on Sturges Road in West Roxbury, filming a commercial. "I asked him: 'Was this a campaign ad he was shooting?' And he said, 'Yes,' " said one neighbor, a supporter of mayoral candidate Michael F. Flaherty who declined to give her name.

Menino said the ad shoot, first reported in yesterday's Boston Herald, was not necessarily what it appeared to be. "We could be doing a promotion about what a great city we have," he said. "It could be a lot of many things."

The demure approach has exasperated the officially declared candidates for mayor.

"Politics can be very strange in this town," Councilor Sam Yoon said yesterday. "A mayor can shoot a TV commercial and hire a campaign manager and not be running and not engage the public in a debate about this city. It's a funny thing."

Mayoral candidate Kevin McCrea, a South End developer, was sharper. "I actually think it's an insult to the citizens of Boston that he essentially holds the city hostage while he decides what he wants to do," McCrea said.

In fact, Menino has often eschewed official campaign announcements with the balloons and sign-waving supporters, preferring to solidify his support with a busy schedule of neighborhood events. Political specialists said the mayor is merely exploiting one of many advantages of incumbency.

"If you're not officially a candidate, people can't treat you like a candidate, so they have to keep treating you like the mayor," said Dennis Hale, a Boston College political scientist. "As soon as you're a candidate, some of the gloves come off, and the questions get a little nastier."

For now, questions about the mayor's political intentions seem to follow him everywhere he goes. Yesterday, speaking to staff members at the Dana-Farber Cancer Institute, Menino effusively praised oncology nurses, saying they are more forthright than oncologists. That prompted the institute's president, Dr. Edward J. Benz, whose wife is an oncology nurse, to joke: "When I tell her what you said, she'll run your campaign."