More than 400 people crowded Arlington County's Courthouse Plaza building last night to urge the county's Planning Commission to reject a proposal to house jail inmates, the homeless and drug and alcohol addicts in a facility next to a South Arlington park.

"We're not going to take this lying down," said David Magruder, who lives near the proposed treatment center's site on South Four Mile Run Drive. "We don't want convicts running around our neighborhood."

County Manager Anton S. Gardner's proposal for a $4.7 million, 130-bed facility that would include 70 beds for minimum-security prisoners has become the most bitterly opposed county initiative in years, drawing criticism from residents who fear that criminals and transients from the facility would venture into nearby Barcroft Park.

Opponents also have accused Gardner of rushing the proposal toward approval by the County Board without enough debate. County officials say the need to relieve crowding at Arlington's jail has accelerated action on the proposal, which was announced early last month and is scheduled to come before the County Board on June 23.

The Planning Commission planned to adjourn early this morning after having heard 30 of 171 residents signed up to speak on the issue. The commission, an advisory panel that will make a recommendation to the County Board, is scheduled to take up the matter again on Saturday.

County officials have said the three-in-one facility would address critical needs. They say the corrections part of the facility would house only those jailed for minor offenses such as shoplifting, driving while intoxicated or possession of small amounts of drugs. Inmates at the center would be in the final year of their sentence and would be gradually getting back into the community through work-release and similar programs, officials said.

Last night's meeting was so crowded that fire officials limited the number of people inside the meeting room to 185. The rest of the crowd grouped around several television sets that carried a closed-circuit broadcast of the meeting.