It is believed they broke in during the night on New Year’s Eve after smashing a window at St Leonards-on-Sea Methodist Church, in Upper Park Road.
The trail of wanton vandalism was discovered by the church steward, Steve Wise, the next morning on New Year’s Day.
He then reported the incident to police.
A spokesman for the church said: “We think they [vandals] broke in during the night on New Year’s Eve.
“They lobbed a pebble through a large double glazed window at the front.
“Probably little damage was caused but it was plain stupidity.
“A keyboard has been overturned and we cannot touch anything until the police have been and investigated.
“The Christmas tree was also overturned, all of the hobs were switched on and they tried to set fire to a crib that was part of a nativity display.
“Straw was set alight and the fire could have spread. The pins from the fire extinguishers were also removed.
“Luckily the oven and hob is electric and was left on for up to 14 hours.
“If it had been a gas oven left on that long, who knows what could have happened?
“Nothing like this has ever happened at the church before.”
A spokesman for Sussex Police said officers are currently investigating the break-in.
Anyone with information should call police on 101, quoting 943 of January 1.