A sticky-fingered Grinch and his accomplice swiped nearly $30,000 in holiday donations from a New York City church yesterday, slipping past two guards and opening a locked safe during a Christmas-morning Mass.

The brazen heist of poor-box funds at St. Mel Roman Catholic Church in the NYC borough of Queens left faithful parishioners shocked and the congregation's pastor, the Rev. Christopher Turczany, looking for answers.

"It's heartbreaking," said Turczany. "The money that comes in, it goes to needy children, and is used to pay the insurance bill - which is due next week - and the electric bills."

He said the 2-foot by 2-foot metal lockbox that was stolen contained all the collections from four previous Masses - at 4 p.m., 6 p.m. and midnight on Christmas Eve and an early 7:30 a.m. Mass on Christmas Day.

While many of the donations were in check form, and would likely be of no use to the thieves, much was also in cash, the priest said.

It remains a mystery how the thieves opened the locked, walk-in safe in the church's sacristy, but two young parishioners charged with guarding the room said they believed they were deliberately distracted.

The sacristans, Nicholas Mangino, 18, and Christopher Urena, 20, said they left their post when they heard footsteps and saw lights flickering downstairs just after the start of the 9 a.m. Italian-language Mass.

"We didn't see anything," said Mangino. "We came back upstairs and found the safe door open and the money missing. We think it was a diversion."

The guilt-ridden sacristans said they'd been put on alert earlier by Father Turczany, who had indicated that he'd seen a suspicious stranger loitering by a rear entrance.

"I'm hurt," said Urena. "How can anyone rob a church any day - especially on Christmas?"

But the thieves may not get far.

The priest said that a parishioner, Rich Chitos, saw the two men - one with what looked like the lockbox in his arms - making his way out the door.

According to Chitos' account, one of the men identified himself as "Dennis" and said he and his accomplice were making repairs to the recently installed elevator.

The brazen thief even shook Chitos' hand and wished him a "Merry Christmas" before disappearing with his friend into a white Lincoln Navigator - but not before a suspicious Chitos copied down the license-plate number.

Cops were tracing that plate last night.

Parishioners at the 65-year-old church tried their best to remain Christian, in their attitude toward the thieves.

"We feel terrible," said Joan Kirk, 80, of Whitestone. "God help those people who did it. I asked God to forgive those people who did it. But I hope they catch the guys."

Not all were quite so charitable, including 81-year-old parishioner Dominick Foglio, of Flushing, Queens.

"If I catch the guy, I break his hands," he said.