Retha and Robert Morgan, who were arrested after plainclothes officers infiltrated a high school graduation party at their Vienna home, pleaded no contest yesterday to charges involving alcohol use among minors, and their attorney said the police had acted appropriately.

It was a major shift for the Morgans, who had bitterly criticized the actions of law enforcement officers and touched off a major debate over how far police should and can go to curb drinking among teen-agers and related highway deaths.

The Morgans said that after initial confusion and anger over the June 12 incident, they realized that the Fairfax County police and agents for the Virginia Alcohol Beverage Control Board had been "well motivated" when they attended their party out of uniform, unannounced and without a warrant.

The Morgans thanked everyone who supported them and said that the experience, while publicly painful, had promoted "a better understanding and a better sensitivity" on all sides. They also noted a "broader community responsibility."

In return for the Morgans' pleas on the charges of aiding and abetting the consumption of alcohol by minors, the Fairfax commonwealth's attorney's office agreed to dismiss the case in six months if there is no violation, and it dropped a separate charge against Retha Morgan of being drunk in public.

"We feel it was a fair disposition for all concerned," the Morgans' attorney, Jerry M. Phillips, said after the brief hearing yesterday at Fairfax County's Juvenile and Domestic Relations District Court. "They {law enforcement officers} acted appropriately."

"I feel relieved that it's finally come to some conclusion," Retha Morgan, 40, said outside the courthouse. "We never wanted to make it an 'us against them,' " added Robert Morgan, 52.

Retha Morgan has said she did everything possible to maintain order at her party, to which 619 graduating seniors in her son's class at Oakton High School had been invited. She said that this effort included informing police in advance and receiving a booklet of party tips from them. She said she posted a sign that said "Please, No Alcohol" in hopes of discouraging drinking.

However, Fairfax police countered that uniformed officers who were patrolling the neighborhood saw several indications that the party was out of control and that minors were drinking alcohol. After the two plainclothes police officers and an ABC agent were sent in, police said, the officers and agent reported that they saw young people "staggering" and that they saw no sign posted.

Police defended the use of plainclothes officers as the most effective way to hold parents accountable for allowing underage drinking on their property. That strategy, used before by Fairfax police but shunned by other law enforcement agencies in the Washington area, appears to be legal, according to several legal scholars.

Fairfax Commonwealth's Attorney Robert F. Horan Jr. has said that historically the Supreme Court has taken the position that "what is readily apparent, in plain view, is fair game." After inviting the entire senior class, it was unrealistic of the Morgans to expect that the party would remain private, Horan said.

The Morgans' attorney agreed with Horan yesterday. "The constitutional issues are not relevant because the party was such that it was open and notorious, and therefore expectation of a right of privacy could not have been claimed," said Phillips.

Asked about the use of young-looking plainclothes officers to infiltrate teen-agers' parties, Retha Morgan said, "I'd have to do a lot more studying and discussing before I could comment on that." But she said she does not approve of the practice.

Phillips said that while the Morgans would have preferred that no officers attend their party, they now understand why the officers did so.

The Morgans "didn't realize that the kids were surreptitiously concealing" alcohol, said Phillips. Retha Morgan "was busy cooking 600 hot dogs."

The aiding and abetting charge, brought by an ABC agent, carries a maximum term of 12 months in jail, a $1,000 fine and the possible loss of driver's license, said Phillips. It was heard in juvenile court because it involved minors, he said.

Under the plea agreement, the case will be dropped if there is no violation in the next six months, said Deputy Commonwealth's Attorney V. Britt Richardson Jr. He said the charge of being drunk in public, which carries a $100 fine, was dropped in General District Court yesterday.

"The disposition was in the best interest of the public and of the defendants," said Richardson. "We felt the police acted reasonably . . . . And at the same time, the defendants appeared to appreciate the issues involving teen-age drinking and public safety, and it appeared their intentions were good."

Although county police did not make arrests at the party, they arrested several juveniles at a roadblock a quarter-mile from the Morgan house in the 10000 block of Old Hunt Road for alcohol or alcohol-related offenses. Those cases are being handled on an individual basis in juvenile court, said Richardson.

Retha Morgan has said that about 3:30 a.m. June 12 she walked to the roadblock to find out what was going on and to see if anyone needed a ride home. Morgan, who was carrying an empty glass, was given and failed several routine sobriety tests, police said. Police Capt. Richard J. Rappoport said she registered 0.16 on a blood alcohol test -- above the presumed intoxication level of 0.10 under Virginia law -- and was ordered to spend the night in jail.

Asked about the public drunkenness charge yesterday, Retha Morgan deferred to Phillips. He said, "She personally contends she was not intoxicated; however, the facts as they've been brought out will speak for themselves."

Asked if she would throw such a large party again, Retha Morgan, the United Way's vice president for national conference planning, said she would do it again but probably would not notify the police.