A proposed curfew for Arlington County children under 16 years of age failed yesterday despite an emotional plea from its sponsor, County Board Member Dorothy T. Grotos, who said it was needed to help stem truancy and drug and alcohol abuse among minors.

"The young people are saying they need help, but the adult community is burying its head in the sand," said Grotos, who appeared close to tears at times as she read statistics she said showed a growing incidence of experimental drug and alcohol use among children.

"Many leave school during their lunch hours and come into contact with drugs . . . ," she said. "I'm concerned with students leaving at noon and not coming back and what condition they're in when they come back."

Grotos' curfew motion failed for lack of a second. Members opposing the curfew said, however, that Grotos' proposal had raised issues that should be pursued through tougher state truancy laws that would augment health and safety laws that already allow police to monitor children in public places.

None of the seven citizens who spoke at yesterday's hearing, the county manager or school officials supported the curfew proposal. They cited difficulties enforcing such a law and the burdens a curfew would place on police, juvenile courts, parents and businesses.

The speakers raised questions about how store owners could get proof of a child's age, whether he went to a private or parochial school which have different hours and holidays from public schools, whether he was an Arlington resident or whether he was out on a legitimate job, such as delivering newspapers.

Although the curfew proposal was not aimed specifically at game parlors, a police report prepared for the board indicated there was little crime that could be traced directly to such arcades and that the crime rate for juveniles under 16 was actually decreasing. Another report from the high school principals suggested that if a law is needed, it should be a truancy law instead of a curfew.

Grotos changed parts of her proposal yesterday in an attempt to make it more palatable. As amended, the measure would have barred children under 16 from such places as parks, restaurants, stores, shopping centers and video or game parlors between midnight and 5 a.m. and between 9 a.m. and 1 p.m. on school days. The proposal would not have applied to children accompanied by an adult or with a valid excuse. Violation would have carried a maximum fine of $500 and 30 days in jail upon repeat offenses.

"This will create hassles and bad feelings between the police, parents, businessmen and minors," said Jerry Mayer, 14, the Washington-Lee High School freshman class president and the only youth who spoke.

"The image of a parent doing 30 days and getting a $500 fine because his kid is playing Pac-Man during lunch is ludicrous," said Tom Hall, speaking for the Arlingtonians for a Better County. "The crime statistics to support such a law have not been presented."

In other action, the board agreed to help the efforts of the St. Alban's Housing Corp. to secure federal funding for a proposed 100-unit residence for the elderly. It agreed to contribute nearly $40,000 worth of county-paid capital improvements at the 600 N. Madison St. site of the proposed residence.