THOUGH IT'S been almost two decades since her teenage son drowned in the raging waters of Pennypack Creek, Mother's Day never gets any easier for Beth Simonetti-Gallelli.

"Don't do this to your mothers. Don't make them talk to your picture and try to remember what your voice sounds like," Simonetti-Gallelli told an auditorium of a few hundred students yesterday at Father Judge High School in Holmesburg, where her son, Nicky Simonetti, 15, had just finished his freshman year in the summer of 1996 when he drowned.

"My son is now officially dead longer than he was alive. He's dead 18 years."

Simonetti-Gallelli delivered her heart-wrenching talk yesterday as part of a series of assemblies in Northeast Philadelphia schools, organized by the Holme Circle Civic Association, to educate students about the dangers of creek swimming.

The assemblies, the first of which took place at Pollack Elementary on Welsh Road near Tolbut Street, and the last of which will be held May 20 at St. Jerome's in Holme Circle, were spurred by the drowning in Pennypack Creek of 13-year-old Brandon Boyle in July, and a Daily News story that month about numerous drownings in Pennypack and other city creeks, including the Wissahickon and the Tacony, over the last several years.

"According to a count by the Daily News, 17 people have died in the last two decades" in creeks, Holme Circle Civic Association President Elsie Stevens said before Simonetti-Gallelli and speakers from the police Marine Unit, Fire Department and Water Department took the microphone at Judge yesterday.

Simonetti-Gallelli looked at the sea of light-blue uniform shirts in Judge's auditorium yesterday and told the boys the story of her son, who took honors classes and rowed for the school's crew team.

"The last picture I have is him in his Father Judge uniform," the mother said.

Nicky's childhood friend, Chris Busse, had been at the creek with him on that fateful day in July 1996 when Busse, whom Simonetti-Gallelli described as a "daredevil," tried walking across the waterfall at the dam in the creek off of Roosevelt Boulevard. Chris fell in, and Nicky jumped in after in an attempt to save him.

Neither boy made it out alive.

"The reality is, if you go in [the creek], you may not come out," a stern Simonetti-Gallelli told the high-schoolers yesterday, adding that 18 years after her son's death, "Nothing has ever been the same since. Everything is a little dimmer. Everything is a little sadder."

Councilman Brian O'Neill's district covers the area of Pennypack Park where a dam creates a pool and a waterfall that often tempt - and claim the lives of - young swimmers. Since Boyle drowned by the Pennypack dam last summer, O'Neill has been working to get grant money to have the dam partially removed.

Because there are Water Department pipes running underneath the dam, he said the estimated cost of the reconfiguration is between $800,000 and $900,000.

He and others involved with the plan, which would slow the currents caused by the waterfall at the dam, are waiting for news this month about a federal grant that could make the project reality.

There's also an environmental reason to remove the dam: It prevents fish from traveling upstream and spawning.

Back at Judge yesterday, Simonetti-Gallellli begged the boys to stay out of the creek this summer.

"If you all love your mothers and your fathers, be safe. You all have such bright futures," she said. "I know what my son would have achieved, and it's not worth it."