Harvard administrators have described the tunnel as a crucial piece of the project that will house the government department and a half-dozen related research centers. Last month, the city’s planning board agreed that the tunnel would make the project a better long-term development.

The board recommended that the city council grant permission for the tunnel. But in the past, the council has frequently disregarded planning board recommendations, said Cambridge political observer Robert Winters.

And he said city planning decisions are more likely to turn into political maneuvering when Harvard development projects are involved.

“Their goal is not necessarily to solve a problem,” Winters said. “It’s also their goal to reinforce their position for the next election.”

Councillors said they have received many e-mails and phone calls from both sides but they say that, on balance, more opinions have come from mid-Cambridge neighbors who oppose the tunnel.

“It’s a very ambitious project, to say the least, and would cause some major disruption to the immediate neighbors,” said Councillor Timothy J. Toomey, who raised objections to the project but said he hasn’t made up his mind to vote against the tunnel. “I always like to listen to both sides, but I’m somewhat skeptical at the moment.”

The University does not have the six votes it needs to achieve a two-thirds majority on the council in favor of granting an easement for the tunnel. But administrators say they are still hopeful that, in the end, they will win over a majority of the councillors.

“I think at the moment we do not have the votes we need, but I do feel that the case for the tunnel is strong,” said Senior Director of Community Relations Mary H. Power.

As part of an effort to make the University’s case, Dean of the Faculty Jeremy R. Knowles has been encouraging professors to attend tonight’s meeting.

“I certainly don’t want to leave the only presence, and the only audible message, to a small group of neighbors,” Knowles said yesterday.

Administrators said their attentions have been so intently focused on getting the tunnel easement approved recently that they have not developed a plan B in case the council denies tunnel-building permission.

“At this point, we do not have a contingency plan because all efforts are focused on the option we have proposed,” Associate Dean for Planning David A. Zewinski ’76 wrote in an e-mail.

The president of the Mid-Cambridge Neighborhood Association—the organization that has long opposed the government center and this winter renewed its objections to the tunnel—said his organization is willing to discuss compromises.

“We’re going to make some proposals to have something other than an up-or-down vote on the tunnel,” said association President John Pitkin.

—Staff writer Lauren R. Dorgan can be reached at dorgan@fas.harvard.edu