If the University decides to build two new residential colleges, the Yale Tomorrow capital campaign’s initial target of $3 billion could swell to as much as $3.5 or $4 billion, according to officials involved with the fundraising effort.

Because it was not listed as one of the campaign’s priorities at its launch in September 2006, the proposed expansion of Yale College is not slated to receive any financial support from the campaign as it stands now, the officials said. Instead, if the colleges are approved later this year, Yale fundraisers are expected to raise at least $500 million more in order to help defray the cost of the expansion, they said.

The campaign would likely be relaunched with a new goal, likely no less than $3.5 billion but possibly as much as $4 billion, according to the officials.

“The goal of $3 billion was set to meet the priorities that we identified at the time, and we don’t want to go back to deans or faculty and say, ‘Well, sorry, we have to take a few things away because we need to raise money now for a new priority,’ ” said Vice President for Development Inge Reichenbach. “That is not what we want to do. That is not what is going to happen.”

The colleges — which the Yale Corporation decided will not be named after donors, no matter how generous they may be — are expected to be the most expensive residence halls ever constructed at Yale or elsewhere in the United States, with a preliminary budget projection of no less than $600 million. On Feb. 23, the Corporation directed University administrators to prepare a strategy for soliciting donations to help underwrite that cost.

Yale Tomorrow, the University’s largest fundraising effort in its history, aims to raise $3 billion by mid-2011. Through the end of February, Yale had raised just shy of $2.1 billion, putting the University at least one full year ahead of schedule in its fundraising.

Raising the campaign’s goal by at least $500 million may not pose much of a challenge; so far, the campaign has netted at least that much million annually in gifts and pledges in both its two-year quiet phase and over the last two years, putting Yale Tomorrow on track to top out at no less than $3.5 billion if the University’s donors do not slow their pace in pulling out their checkbooks.

In interviews this semester, University officials acknowledged for the first time that the original $3 billion goal was a somewhat conservative target, and that officials estimated the capacity of Yale’s donor base at a higher figure. Some observers had raised questions about why Yale’s campaign goal was $3 billion when some of its peer schools were launching much more ambitious efforts. Stanford is in the midst of raising $4.3 billion, while Columbia and Cornell are each seeking $4 billion.

In a recent interview, Roland Betts ’68, senior fellow of the Yale Corporation and a co-chair of Yale Tomorrow, recalled a conversation he had with a skeptic who inquired why Yale was not setting the bar any higher for its campaign, especially when compared to other schools.

“Let’s assume that each school raises $3.5 billion,” Betts said, citing the example of Yale compared to another school. “You would say each school has had identical performances, right? But Yale would be perceived as being wildly successful, and [the other school] a dismal failure.”

He added: “You never want to have a target that you don’t reach. You never want to do that.”

University officials expressed hesitance at speculating on the exact figure that could become the campaign’s new goal as the Development Office is still in the process of making that assessment in advance of the Corporation’s next meeting.

But administrators indicated that any target in the range of $3.5 billion to $4 billion would be conceivable.

“We’re addressing the issue right now,” University President Richard Levin said Thursday. “We need to think about raising the goal. We’re assessing the feasibility of doing so.”

The Corporation, the University’s highest governing body, will next convene on campus April 10 through 12. During its meetings last month, the Corporation asked the Development Office to conclude its analysis of how the University might solicit gifts to defray the cost of the expansion.

The Corporation also requested that University administrators prepare a preliminary budget for both the construction of the colleges and the operation of an expanded Yale College. A very high proportion of the bricks-and-mortar cost to build the new colleges would likely be funded by donors, Betts said. The increased operating expenditures, meanwhile, will be covered, at least in part, by increased spending from Yale’s $22.5 billion endowment.

A final decision on whether to proceed with the expansion could come at the Corporation meeting in April or June. The expansion, which would include the construction of two new colleges behind the Grove Street Cemetery on Prospect Street, would boost Yale’s undergraduate enrollment by more than 10 percent.