The last four months have given Scott Keenan plenty of time to think about the bar business and the difficult task of thwarting underage drinkers.

His North Wildwood bar, Keenan's, which encompasses an entire city block, has been closed since Sept. 3, 2008, when New Jersey's Division of Alcoholic Beverage Control ordered the bar's retail license suspended for 80 days for underage-drinking violations.

"We're not saying we're innocent," said Keenan, 36, of South Philadelphia. "There's a problem with the system."

The system, Keenan says, punishes the bar owners far more harshly than the person using the ID and committing what he believes amounts to fraud.

As he shuffled the 175 fake IDs he confiscated at the bar from Memorial Day to Labor Day last year, Keenan said that he knows that most of the people who used them are probably a little miffed that they were taken, but otherwise are living life as usual after paying a fine and, possibly, experiencing a six-month suspension of a driver's license.

Starting today, when Keenan's officially reopens, things are going to change, he said: Earlier this week, the bar sent letters to at least 13 people who either had gained entrance or had tried to get in with a fake ID over the past five years.

"We would like to hear from you or your legal representative within the next 20 days regarding this fraud," the letters said.

Those people paid a combined $5,750 in fines, and only four of them were given six-month license suspensions. By contrast, Keenan said, the bar paid more than $300,000, not including lawyers' fees.

"The kids use these IDs because the consequences aren't that significant," Keenan said.

Jack Keenan, Scott's father and co-owner of the pub, said he hopes that the letters prove a point to the underage drinkers, to the people who may have given them IDs and, particularly, to the state ABC office.

"We're trying to send a message out there that we don't need underage drinkers and we don't want them," said Jack Keenan, 65, a former vice president of a roofing-supply company based in Philadelphia.

New Jersey runs a "Cops in Shops" program to help catch underage customers buying beer at liquor stores. Jack Keenan said that he's been talking with local and county law-enforcement agencies to do the same in bars.

Doormen at Keenan's are armed with UV flashlights to detect hidden insignias on real IDs. If they're still wary, customers are asked to sign affidavits and leave IDs in a little plastic box at the door.

"They have more doormen than anyone else," said North Wildwood Mayor Bill Henfey. "Sometimes, somebody will get through."

Henfey and North Wildwood's police chief both support the Keenans' efforts to deter underage drinkers, and both are aware of the difficult task that they and other bar owners along the popular Olde New Jersey Avenue strip face.

"Could the state come up with a secure ID for people in the 21-to-25-year range?" Henfey asked. "Then maybe the bars could purchase a scanner or reader? Outside of that, I don't know what they could do."

Mindy Lazar, executive director of Mothers Against Drunk Driving in New Jersey, commended Keenan for being proactive but said that he needs to follow through with threats.

"Anything and everything that is possible for a shop owner to deter underage drinking is a plus," she said.

Henfey said that he tried to intervene for Keenan's when the bar was ordered to close just weeks before the most profitable weekend for all bars in town, the annual Irish Fall Festival.

Keenan said that the state agreed to let him remain open for the festival, which draws more than 200,000 people, but that the stipulations were too strict: No one under 25 could be admitted, additional penalties would have to be paid, and the bar would have to close from mid-May until June 30 this year.

North Wildwood Police Chief Robert Matteucci said Keenan's has submitted a proposal to the planning board that would allow modified entrances to "provide for better monitoring of patrons entering the premise."

When asked to comment about a bar owner's responsibility in underage-drinking cases, the ABC directed the Daily News to "the criteria for avoiding an underage-sale violation" in its handbook.

According to the ABC handbook, a bar or liquor store has a defense if it asked for and receives both a license and a government or state photo ID, a written affidavit signed by the customer; and, finally, the seller must believe that the customer was 21 based on real or false ID.

"If there is any doubt that the purchaser is under 21 years of age, the sale should not be made," the handbook reads.

One of Keenan's infractions, Scott said, came from a father giving his daughter alcohol at a school reunion: The bar hosts several reunions every summer for various Catholic schools in the region.

"It's disheartening because we don't encourage it, and I think that was the perception of the ABC at one point," he said.

During the bar's hiatus, Scott Keenan said, he's had to fight rumors that he was selling the business, to calm fears from folks who were skittish about booking large events this summer.

"I'm in this for the long haul," he said. "I'm hoping that in 20 years my son's behind the bar."

The crowds will be small and mostly older at Keenan's until Memorial Day, when throngs of college students and summer rentals make their way toward the Wildwoods. On any given weekend night, Scott said, his 25,000-square-foot pub could get from 1,000 to 3,000 customers.

Keenan's and its summertime staff of more than 50 will be ready for them. Potential customers under 21, even one out of those thousands, should be ready, too, he said.

"I'm going to get some of those Violators will be Prosecuted signs," he said. "I'll grab a few at Home Depot."