Anna Phelan and Emily Adams wanted to end their four years at Bethesda-Chevy Chase High School with a memorable backyard graduation party.

There was a blues band, a moon bounce, a popcorn machine and a pit for making s'mores. Guests feasted on hot dogs, hamburgers and bratwurst. There was plenty of ginger ale, cranberry juice and root beer to go around. What there wasn't plenty of was alcohol.

"It was pretty low-key, and it was just sweet," Margaret Engel Adams, Emily's mother, said of the party for about 80 friends and relatives. "It was just pretty much out of Norman Rockwell."

All that changed about 9:30 p.m. Thursday, Adams said, when a Montgomery County police officer knocked on the Phelans' door, in the 4600 block of Rosedale Avenue in Bethesda, to say that someone had complained about the noise. The officer then asked Anna's mother, Kathy Phelan, if he and several other officers could give breath tests to the teenagers. She refused.

So police stationed patrol cars at each end of her street, six in all, and began giving the tests to guests as they left the party, she said. None of the teenagers tested positive for alcohol, she said.

Officers then began ticketing vehicles parked outside the Phelans' house, she said, including ones that belonged to neighbors who weren't at her party. Some vehicles were ticketed for a wheel improperly touching a curb or for extending into a driveway. Emily Adams, 18, received a $35 parking ticket; her Honda Odyssey minivan was parked directly in front of the Phelans' home.

"It almost seemed like they were angry that they didn't find anything," Kathy Phelan said.

The officers were part of an Alcohol Enforcement Section that combs the county around holidays and during prom season to guard against underage drinking. The eight-officer unit checks bars and restaurants and responds to citizen complaints when house parties appear to involve underage drinking.

"When they get calls that there may be underage drinking, their response is to investigate it," said Lt. Eric Burnett, a police spokesman. "We're trying to prevent teen deaths."

Margaret Adams and Kathy Phelan have written a letter to Montgomery Police Chief J. Thomas Manger and several other county officials. They are seeking disciplinary action against the officers and apologies to their daughters, best friends since middle school who graduated from Bethesda-Chevy Chase High School on Wednesday.

Burnett said that it was too early to discuss the allegations of the party hosts but that the incident was under investigation and that any proven misconduct would result in disciplinary action.

He said it is standard procedure for alcohol enforcement officers to cordon off a block if they are denied access to a property where they suspect underage drinking is happening. He added that the parking infractions described in the letter "are tickets that you can actually receive. We can't just make this stuff up."

Phelan said police never asked her if there was alcohol in the house. There was a small amount of beer at the party -- for adults -- but it was kept in the kitchen. The teenagers couldn't get to it without walking past an adult, she said.

John King, assistant Montgomery police chief, said the alcohol enforcement officers had "some indicators" of underage drinking at the party. "But it turned out those indicators were wrong."

Ryan Hamm, 17, said he was tested as he walked from the house to his car. No alcohol was detected, he said.

"We were like making s'mores in the back and they had cake," he said. "It was just like people talking and a band playing, and it was fun."