With the community on heightened alert after Saturday's bombing of Centennial Olympic Park in Atlanta, local authorities were called in to investigate two suspicious bags over the weekend, both of which turned out to be harmless.

State and local authorities cleared the northern half of John F. Kennedy Park Sunday to examine an unattended knapsack.

A witness saw a suspicious-looking man drop the knapsack in the park and run out of the park and over the Anderson Bridge into Allston, police said.

The man was apparently wearing a dark blue suit and sunglasses, police said.

"It was more the method of what he did--he left it there and he put it down and ran away," said a Harvard police officer on the scene who declined to give his name.

State and local police cleared the area around the knapsack, creating a circular open space with a radius of about 50 yards.

As authorities waited for the bomb squad to show up, some Sunday park-goers watched with apprehension, but others continued frolicking and playing volleyball and frisbee on the other side of the park.

"I trust the police," said Gregory J. Rooker, a rising sophomore at Boston University who was playing volleyball in the park. "If they say it's all right, it's all right. And look--it's a beautiful day for some sun and some v-ball."

Cambridge Detective Chuck Mottola arrived about 20 minutes later to inspect the knapsack.

Mottola first examined the knapsack from a distance of about 10 feet. Noticing no protruding wires, he advanced carefully, peered inside and discovered only some old newspapers.

He gave the police and the crowd a thumbs-up to signal that all was well, and those in the park who were watching gave him a standing ovation.

Despite the false alarm, Mottola said in an interview that citizens should remain on heightened alert.

"You just never know," he said. "Anything can be an explosive device or an incendiary device, and you have to be careful."

Mottola did say that local authorities were being especially cautious in the wake of Saturday's bombing of Centennial Olympic Park and this month's explosion of TWA Flight 800, both of which are being attributed to terrorism by some authorities.

"I think it has everyone on heightened alert," Mottola said of recent bombings.

The second false alarm of the weekend was much less dramatic.

The episode took place just a few minutes later in Au Bon Pain.

According to Harvard Police Sergeant Robert A. Jones, a patron of the restaurant left some belongings in a bag on a table while "getting a sand-wich."

A security guard picked up the bag and called the police. The bomb squad soon arrived to defuse the situation.

Jones refused to comment further, and no other details were available yesterday