As several dozen football players sweated on a practice field yesterday, a group of their Northgate High School classmates played another brand of defense.

Members of the school's SADD chapter gathered to promote a nationwide crackdown on drunken driving that began yesterday, with an emphasis in Pennsylvania on curbing underage drinking.

"It's definitely an issue. It's a growing issue. That's why we're becoming so active in trying to stop it," said Julia Lauria, a Northgate junior.

The students were joined by state police and officers from Bellevue, Moon, Baldwin Borough and Pittsburgh. They will be on the offensive until Labor Day, with increased patrols and sobriety checkpoints.

"We're out to give the impression of omnipresence," said Moon patrolman Douglas Ogden. He said the West Hills Area DUI Task Force will set up four checkpoints during the crackdown period, augmented by roving patrols watching for those who try to elude them.

"I know where the escape routes are and where people try to go around us," he said.

Officer Ogden said he's never been part of a checkpoint that didn't collar at least one inebriated motorist, and usually they'll snare eight to 10.

He and Sgt. Terry Donnelly of the Pittsburgh police recalled a checkpoint on Route 65 at Marshall Avenue that netted 25 DUI motorists in three hours.

Some 6,000 municipal police forces in the state are expected to take part in the crackdown, joined by state police, who plan a 50 percent increase in patrols, according to Trooper Robin Mungo.

"There will be more officers out, more eyes out. We want people who aren't impaired to feel safe on the highways. The biggest thing for us is to be out there, be seen, and make people think twice" before drinking and driving, she said.

The Pennsylvania DUI Association has begun a campaign to reduce underage drinking and driving. It is called "U-Turn" and has a Web site, pullayouee.com, and Facebook page at facebook.com/PaUturn.

The intent is to let young people "connect with each other and let it be known that they aren't alone in being alcohol-free," said Felicity DeBacco-Erni, statewide program director for SADD, Students Against Destructive Decisions.

"Underage drinking is one of our top public health problems in Pennsylvania," she said.

There were more than 1,400 alcohol-related crashes involving drivers ages 16 through 20 across the state last year, resulting in 45 deaths, the Pennsylvania Department of Transportation reported.

Under the state's zero-tolerance law, persons under 21 convicted of driving under the influence with a 0.02 blood alcohol level or higher face a 12- to 18-month license suspension, two days to six months in jail and fines of $500 to $5,000.

Additionally, anyone under 21 convicted of consuming, possessing or transporting alcohol, lying about their age to obtain alcohol or carrying a fake ID is subject to a $500 fine plus court costs and a 90-day license suspension for the first offense.