Former Virginia first lady Maureen McDonnell, center, leaves federal court with her sons, Bobby, left, and Sean after her husband, former governor Robert F. McDonnell, was sentenced to two years in federal prison for corruption charges on Jan. 6. (Daniel Sangjib Min/AP)

The U.S. probation office has determined that federal sentencing guidelines call for former Virginia first lady Maureen McDonnell to spend as long as 6 1/2 years in prison — a stiff term that she is unlikely to receive but one that will nonetheless serve to guide the judge deciding her fate.

In a sealed report given to prosecutors and defense attorneys last week, the probation office wrote that it had calculated McDonnell’s guideline range as 63 to 78 months — roughly 5 to 6 1/2 years in prison. Two people familiar with the report’s contents described the range on the condition of anonymity because the matter has not been made public.

U.S. District Judge James R. Spencer is required to consider that range as he sentences the former first lady Feb. 20, although he is not bound to follow it. This month, Spencer sentenced former Virginia governor Robert F. McDonnell, Maureen McDonnell’s husband, to just two years in prison, despite an initial recommendation from the probation office that the onetime Republican rising star spend at least 10 years and a month in prison.

Legal experts have said Maureen McDonnell’s sentence is likely to be less than her husband’s, given that the former first lady was not considered a public official and was found guilty of three fewer public corruption counts.

Defense attorneys for Robert and Maureen McDonnell, U.S. Attorney Dana J. Boente and a federal probation official in Richmond declined to comment for this article.

The McDonnells were convicted in September of lending the prestige of the governor’s office to Richmond businessman Jonnie R. Williams Sr. in exchange for $177,000 in loans, gifts and luxury goods. In the federal system, determining an appropriate punishment for those crimes is a complicated process that combines technical calculations (such as the value of what they received from Williams) with more intangible considerations (such as what might deter others in the McDonnells’ shoes).

Calculating the range of the federal sentencing guidelines is the first step in the process, requiring the U.S. probation office to look at the circumstances of the case and other factors to come up with an objective, mathematical recommendation for what penalty Maureen McDonnell should face. The recommendation is only an initial figure: prosecutors and defense attorneys still can try to convince the probation officer to change the range, and they can eventually take any concerns they have to Spencer.

Ultimately, Spencer will decide what range the guidelines recommend and whether he wants to follow that recommendation.

It is not clear, precisely, how the probation office determined that Maureen McDonnell should spend as long as 6 1/2 years in prison. Those who described the report to The Washington Post did not provide such details. But her husband’s guidelines might be instructive.

The probation office had initially determined that Robert McDonnell received more than $121,000 worth of benefits from Williams — a value that considerably enhanced the guideline range for his sentence — although Spencer said the probation office should have calculated the amount as between $97,000 and $121,000. Spencer also determined — contrary to the probation office’s view — that Robert McDonnell did not obstruct justice in his testimony at the trial and said the guidelines should have called for a prison term between 78 and 97 months, or roughly 6 1/2 to 8 years.

That was significantly less than the probation office’s recommended term of 10 years and a month to 12 years and 7 months

Spencer, of course, gave the former governor a sentence far below what the guidelines called for and spoke at length in court about not being bound to follow those guidelines. At one point, he said a sentence of seven or eight years would be “ridiculous, under these facts.”That was somewhat surprising; judges in the Eastern District of Virginia follow the sentencing guidelines more than 70 percent of the time, and Spencer is known to do so as often as any other judge.

Robert McDonnell’s defense attorneys had asked that the former governor be sentenced to just 6,000 hours of community service. Maureen McDonnell’s attorneys have not yet put together their request to the judge, but they are expected to do so in the coming weeks.

Robert McDonnell is to report to prison Feb. 9 but has asked the U.S. Court of Appeals for the 4th Circuit to let him remain free while his appeal is pending.That effort gained two significant supporters Tuesday, when retired federal judge Nancy Gertner and Harvard law professor Charles J. Ogletree Jr. requested to file amicus briefs backing the former governor. Five former Virginia attorneys general and the National Association of Criminal Defense Lawyers have made similar requests.

Rosalind S. Helderman contributed to this report.