The government's Feb. 16 offer authorizes up to $8.3 billion in loan guarantees, of which Southern Company subsidiary Georgia Power -- which owns a 45.7-percent stake in Vogtle -- would borrow up to $3.4 billion.
Southern Company CEO David Ratcliffe mentioned the extension request in a conference call this week with investors.
"We have until mid-May to accept the nonbinding conditional commitment," he said, according to a recording of the briefing posted Thursday on the company's Web site. "Discussions are under way to secure a one-month extension to the schedule, which will give us more time for due diligence."
Company spokeswoman Valerie Hendrickson said the request was made to secure more time to negotiate an extremely complex agreement.
"It's a good working relationship and we're just trying to work out details," she said. "We are absolutely confident of an agreement very soon."
Ebony Meeks, an Energy Department spokeswoman in Washington, said the request is not unusual and likely will be granted.
"While the standard deadline is 90 days from the date offered it is quite common for applicants to ask for a short extension to continue considering the department's offer," she said.
Other owners of the Vogtle project are Oglethorpe Power Corporation (30 percent), Municipal Electric Authority of Georgia (22.7 percent) and the City of Dalton, Ga., (1.6 percent).
Construction of the reactor buildings, which would create up to 3,500 jobs during peak activity, cannot start until the Nuclear Regulatory Commission issues a combined operating license for the project, which is expected to happen in 2011. Preliminary site work is under way.