An earlier version of this story mischaracterized the proposed disposition of the county-owned site as a sale. The land will be transferred to a public-private partnership but remain county property.

Montgomery County’s joint venture with a private developer to create a new health-and-science town center in its long-overlooked eastern sector has snagged over County Council concerns that the proposed first phase of the plan relies too heavily on new residential construction.

Council members also said Tuesday that they wanted to see the final agreement between County Executive Isiah Leggett and Percontee, the developer, before approving transfer of a 115-acre county-owned site to the public-private partnership that would build “LifeSci Village.”

The council approved the White Oak Science Gateway Master Plan in July. County officials and Percontee, led by Executive Vice President Jonathan Genn, envision an employment hub for medical and life-sciences companies, drawn to the site near Route 29 and Industrial Parkway because of its proximity to the Food and Drug Administration’s White Oak campus.

Officials estimate that synergies between the village and the FDA could create as many as 10,000 jobs over the next quarter-century. The hope is that the project will jump-start the economy of an area that has missed out on the heavy public and private investment in other parts of the county, such as Silver Spring and Bethesda.

Since passage of the broad-stroke master plan, Leggett and Percontee have been working on the gritty details of implementation that will be included in a legal document called the General Development Agreement. Prior to passage of the master plan, then-Economic Development Director Steve Silverman assured the council that it would have “a seat at the table” as the agreement was drawn up.

Leggett aides have been pushing the council to approve disposition of the property as soon as possible. They told the council Tuesday that the agreement will be difficult to complete until the council votes to transfer the county property to Percontee, which owns an adjacent 185-acre tract. But members expressed reluctance to give up their leverage until they know exactly what will be included in the agreement.

“I am unwilling to approve the property disposition until I have real assurances about how this is going to play out,” said council member Roger Berliner (D-Potomac-Bethesda)

Council member Marc Elrich (D-At-Large) concurred. “I’m not going to continue going down this unending rabbit hole” without seeing the development agreement, he said.

Leggett’s representatives at the hearing, Assistant Chief Administrative Officer Tom Street and Deputy General Services Director Greg Ossont, said they would have to confer with Leggett before agreeing to give the finished agreement to the council.

Several expressed unhappiness with the top-heavy residential component in the first phase of the plan. Leggett has proposed to allow up to 1.8 million square feet of residential construction, roughly 1,200 residential units, most likely townhouses. Genn, who did not return a phone call requesting comment Tuesday, has told county officials that the residential construction is an essential precursor to the office and retail development that would follow.

Council members are concerned that Percontee is focused on building homes because the profits are more immediate and the market for new office space is currently moribund.

Council member Nancy Navarro (D-Mid-County) said the heavy first phase of home construction turns the whole idea of the gateway plan on its head. East County has plenty of housing, she said. What it needs is jobs.

“I’m quite frustrated,” Navarro said. The idea “was never to bring in a high concentration of residential.”

County Council staff also objected to the high volume of residential and offered a series of recommendations, including that Percontee be limited to 300 homes until plans are in place for at least 200,000 square feet of office, lab or educational-institution construction.

Council members said they would continue the discussion of the issue after receiving answers to a list of questions they have submitted to Leggett.