The Yale Corporation declared its support this weekend for building two new residential colleges, directing administrators to move forward with planning for the University’s largest expansion in decades.

At their meeting on Saturday, members of the Corporation, Yale’s highest governing body, commissioned two additional studies in preparation for a final vote on the expansion proposal later this year. University administrators will now devise an estimated budget for the two new colleges — which will likely be the two most expensive residence halls ever constructed in American history — as well as a plan to solicit donations to help pay for them.

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And for the first time, the Corporation acknowledged what students and faculty for months have assumed: The members of the University’s highest governing body are fully in favor of expansion.

“I think there is a presumption that this is the right thing to do,” said Roland Betts ’68, the Corporation’s senior fellow, in an interview on Saturday.

“And,” he added, “there is a certain presumption that we are all collectively smart enough to figure out a way to do it so it doesn’t in any way compromise the Yale that all of us know and love.”

In his first public comments on the prospect of building two new colleges, Betts said the Corporation was behind the expansion proposal — and has been for around three years.

“If you’re ever going to expand, this is the right time to do it,” Betts said. “You have an unbelievably precious resource here called the Yale education, and you sort of have a duty to provide it to as many people as you possibly can.”

The decision to proceed was widely expected, especially after University President Richard Levin publicly endorsed the expansion plan in a statement to the community last week. The Corporation did not hold a vote on the matter, instead reaching a consensus to continue planning, Betts said.

Levin was absent from the meeting after the death of his brother on Wednesday. A memorial service was held Sunday in Los Angeles, and the president is expected to be back on campus today. He was unavailable for comment this weekend.

The expansion plan, which has been in the works for a decade but not announced for public consideration until last February, calls for two residential colleges to be erected along Prospect Street behind the Grove Street Cemetery, a location that has been criticized by students as isolated from the central campus.

Only one in four students supports the expansion plan, according to a campus-wide poll conducted by the News earlier this month. Many students have argued that expanding, especially given the location in question, could ruin the quality and intimacy of the Yale College experience.

Still, Betts defended the Corporation’s enthusiasm for expansion.

“What it means to be a trustee at an institution like this is you are the steward of that institution, and you have to exercise your best judgement as to what’s best for that institution and cross your fingers that you’re right,” he said.

He added: “It’s not the students’ decision to expand or not.”

The new colleges would enable the University to ease overcrowding in the existing 12 residential colleges and also to bump up undergraduate enrollment by more than 10 percent, to about 6,000 students in total. A preliminary budget estimate placed the cost of the colleges at no less than $600 million in total.

But Provost Andrew Hamilton dismissed that figure as an extremely imprecise estimate and said that his office, with the assistance of Vice President for Finance and Administration Shauna King, will need to develop a much more exact estimate for the Corporation to consider in the coming months.

Whatever the cost may be, Yale’s donors will cover most of it, Betts said. The Development Office will now prepare a fundraising plan for the colleges, as per the Corporation’s directive.

The University is already in the midst of a $3 billion capital campaign, dubbed “Yale Tomorrow,” which was unveiled to much fanfare in September 2006 and aims to reach its goal by mid-2011.

The campaign does not include the expansion proposal among its goals, although the News reported last spring that administrators had already begun meeting with Yale’s wealthiest donors to discuss the new colleges.

More than $2 billion has already been raised toward Yale Tomorrow’s goal, although donations to Yale fell by 10 percent last year, according to a national survey released Wednesday.

But that decline — which officials said was the result of the timing of gifts and was not an accurate gauge of alumni support — should not cast doubt on Yale’s ability to raise funds for the colleges, Levin said last week.

In fact, the campaign is a full year ahead of schedule, according to Vice President for Development Inge Reichenbach.

The Corporation, meanwhile, will vote on whether to build the colleges either in April or in June. The specific timing of the vote will depend on whether Corporation members are satisfied with their scrutiny of the budgetary and fundraising studies at their next meeting in April or want more time to further examine the expansion plans, Betts said.

But, regardless of when the vote happens, it will likely be more of a technicality than anything else.

“I think it is fair to say that the consensus has developed that we are on the right path, that this is the right idea,” Betts said. “But we’ve got to be certain that we do it the right way.”