Plans for a mass meeting of Arlington Democrats Monday night were thrown into confusion yesterday after party officials disclosed they had failed to properly advertise the session.

The meeting, scheduled for 7:30 p.m. Monday at Kenmore Intermediate School, was supposed to allow the county's Democratic Party to decide whether to endorse or nominate the two men seeking Democratic support for two county board seats at stake in the November elections.

But yesterday, Democratic Committee Chairman Sharon Davis said the meeting's status was in doubt because of "a stupid clerical thing we should have done."

Virginia Democratic Party rules require that such meetings be advertised in a general circulation paper 10 days in advance. The Arlington Democrats' ad, however, did not run until Wednesday, six days before the meeting.

Last night, Davis and 10th District Party Chairman Charles W. Rinker said the meeting would be held as scheduled Monday. They said they believed the session could decide whether to nominate or endorse candidates. But they added that the Democrats may have to hold another meeting before June 14 if the party decides to nominate candidates rather than endorse them.

Arlington candidates often run as independents with party endorsements rather than with party nominations because that arrangement allows government workers to participate in their campaigns. Under the Hatch Act, federal workers, who comprise a large percentage of the county's voters, are prohibited from working in partisan politics.

Only two candidates' names are expected to be placed before the Democratic meeting: Richard A. Buffum, a retired CIA foreign affairs analyst, and Albert C. Eisenberg, director of government affairs for the American Institute of Architects. Eisenberg is married to Davis.

If the meeting decides to endorse the two, Davis said, no further meeting may be required because the Virginia Democratic rules requiring advance notice do not cover endorsements. Buffum has indicated he wants to be endorsed but Eisenberg has said he would prefer to be nominated for the county board. Both have agreed to abide by the meeting's decision.

"I take full responsibility for the mistake ," Davis said. Other Democrats said Davis was out of the country for two weeks recently, and was not responsible. "The Arlington Democratic Party prides itself on being pristine, meticulous and following the rules. So naturally we are all mortified beyond belief that this happened," Davis said.

Republicans will pick their candidates for the seats, currently held by the GOP's Walter L. Frankland and Dorothy T. Grotos, during a canvass of party members to be held Tuesday from 2 to 8 p.m. at the Lyon Village Community House. Frankland, school board member Michael E. Brunner, and John Marshall, an Education Department executive, are seeking the GOP's backing.