A Long Island Marine killed on the battlefield in Iraq was mourned yesterday as a courageous warrior and a steady leader - a man who could deliver a joke as easily as an order.

Hundreds of friends and relatives filed past the open casket of 1st Lt. Matthew Lynch, who was dressed in a pressed blue uniform covered with medals of valor.

Lynch, 25, of Jericho, died Oct. 30 when the convoy he was leading was hit by a roadside bomb in Ramadi. It was his third tour of duty in the war-torn country.

"We want to share Matt's courage with the world," said Lynch's heartbroken brother, Tim, 27, a former Marine who also served in Iraq.

Matthew Lynch could have played it safe and stayed at his base in Camp Pendleton, Calif., but he volunteered to go back to Iraq in August to join his buddies in the 2nd Battalion, 5th Marine Regiment.

"He really fought hard to make his way back to the 2-5," said Lt. Stephen Lewis, 26, of Michigan, who served under Lynch during the fallen soldier's second Iraq tour.

Lynch displayed impressive leadership skills when he joined the 1st Battalion, 5th Regiment, filling in for a platoon leader who was wounded in battle, Lewis said.

"Someone trying to walk in and take command is not the easiest job," Lewis said after Lynch's wake at the Vernon C. Wagner Funeral Home in Hicksville. "But Matt was such a calm, cool leader, so very personable. He did an amazing job."

Lewis said Lynch led his platoon through many skirmishes on the front lines and never lost his composure.

"We had some bad situations. Nothing ever got him riled up," Lewis said.

Retired Marine Capt. Mike Scotti, 28, of Manhattan, said he could understand why Lynch volunteered to go back to Iraq to join the 2nd Battalion, 5th Regiment, the unit he helped train and served his first tour with.

"I've got a lot of friends over there. I feel guilty," said Scotti. "You think you're out, but the war never leaves you."

Matt Hunter, 23, of Baldwin, said he recognized Lynch as a natural-born leader, even when they were both lifeguards at Jones Beach.

"He always had a smile on his face," Hunter said. "He was always joking.

"I never heard an evil word come out of his mouth, except when you screwed up or when you were late," Hunter added. "He was like a big brother, who was looking out for you."

There will be a 10 a.m. funeral Mass for Lynch today at St. Paul the Apostle Church in Brookville, followed by burial at Long Island National Cemetery in Farmingdale.