If Rep. Vito Fossella (R-N.Y.) is unable to reach a deal with prosecutors on his DUI arrest, he will likely have to serve five days in jail before the end of the year, making him only the fourth sitting member of Congress to be locked up following a criminal conviction and dragging his troubles back into the spotlight just as Republicans were counting on them having vanished.

Not since Rep. John Dowdy (D-Texas) was sent to prison for his 1972 conviction for bribery, obstruction of justice and perjury has a sitting member of the House been sentenced to jail or prison following a criminal conviction, according to the House historian.

Under state law, any resignation before July 1 gives New York’s Democratic Gov. David Paterson the option of calling a special election. And Republicans have lost three special House elections since March. If Fossella resigned after July 1, there would be no special election and the seat would remain empty for the remainder of the term.

Fossella’s Staten Island seat is seen as a traditional GOP stronghold in the New York City area.

On Wednesday the House ethics committee formally voted to establish an investigative subcommittee to probe Fossella’s DUI. The committee recommended deferring its inquiry until Fossella’s criminal case is resolved.

Fossella has indicated to the court that he intends to plead not guilty to his May 1 DUI. His case is scheduled to go to trial on June 27.

Legal experts say the threat of jail is still very real for Fossella, and almost certain to happen before year’s end if ordered by a judge as part of a conviction.

Police reports from Fossella’s May 1 arrest in Alexandria, Va., indicate that the New York Republican submitted to two Breathalyzer tests — one after he was pulled over for running a stoplight at the corner of Seminary Road and Library Lane and a second following his physical arrest.

According to police, Fossella’s blood alcohol content (BAC) was initially recorded at 0.13, but was later recorded at 0.17 on what police described as a more reliable machine.

Both are above Virginia’s legal limit of 0.08. But only Fossella’s second alleged BAC of 0.17 is above the 0.15 BAC that triggers an automatic five-day jail sentence in the commonwealth.

“If the prosecution chooses not to offer anything … and the breath certificate comes into evidence, then he will do the five days,” said Bob Battle, who has over 20 years’ experience as both a DUI prosecutor and defense lawyer in Virginia. “That’s not even in play.”

But the dual Breathalyzers could give prosecutors an incentive to attempt to prove Fossella’s guilt through other means, notably the arresting officers’ observations, which would take the prospect of jail time off the table, Battle and other DUI defense experts said.

“It’s not a surprising thing to have a prosecutor use his or her discretion to let a defendant plead to a first-offense DUI with a low BAC, especially in cases in which the [breath] certificate is in question,” said David Oblon, a criminal defense lawyer who specializes in DUI cases in Virginia.

A plea to a first-offense DUI would force Fossella to surrender his license for one year but would get him out of jail.

“I think it will all come down to whether there are any problems with the breath machine,” Battle said. “If there are some issues, I think he’ll get an offer of no jail time. If there are no issues, I think the prosecution will stick to [its] policy and require the five days in jail.”

Alexandria City Prosecutor Randy Sengel on Thursday said he would not comment on any of the evidence involved in the case, but reiterated his statement that prosecutors are not looking to strike a deal.

“Our practice in all DUI cases is not to reduce charges and negotiate into plea agreements for lesser included offenses,” Sengel said.

If Fossella is convicted and his BAC is found to have been above 0.15, he will be required to begin his jail sentence almost immediately.

But Fossella reserves the right to appeal a conviction, which, in Virginia, would automatically negate the original conviction and any sentence attached to it.

An appeal to the circuit court would likely take one to two months to resolve, lawyers said. A conviction in circuit court could be appealed as well, but would not negate a jail sentence if a judge or jury imposes one.

An attorney for Fossella would say only that his defense team plans on mounting a vigorous challenge to the charges against the congressman.

“Obviously Congressman Fossella has apologized and admitted that he made a mistake,” said Barry Pollack, one of Fossella’s attorneys. “The legal issue is whether or not he was actually over the legal limit, and that is what is going to get resolved through the court process.”

House GOP leaders said Fossella “made the right decision” when he announced on Monday he would not run for reelection. Fossella’s announcement came almost three weeks after his arrest and the subsequent revelation he has an out-of-wedlock child.