BOSTON (AP) _ Paul Tsongas' decision to make do without donations from political action committees will likely cost his presidential campaign $500,000, his chief fund-raiser said Sunday.

The move already has cost the campaign close to $70,000.

''I held on to the checks for a while to see if he'd change his mind,'' Nicholas Rizzo said in an interview. ''But he was very firm on it.''

Tsongas, the only Democrat officially in the race, announced Saturday he will refuse all PAC donations because they place the interests of certain groups above those of individual voters.

''I want to win with the freedom that I can go in there and represent all the people of this country and not have to worry about what particular interest groups think about my stand on an issue,'' the former Massachusetts senator said.

In his past congressional races, Tsongas took money from groups representing environmentalists and unions, and from the political committees of other elected officials.

The decision to forgo PAC money may draw attention to the little-known candidate, but it will cost him much-needed dollars, said Rizzo, who is volunteering with the campaign until a finance director is hired.

''We had anticipated $150,000 (in PAC money) in this quarter,'' Rizzo said. ''That's out the window now. And at this late date, there is no way of making that up.''

Rizzo said Tsongas' campaign has a fund-raising goal of between $9 million and $12 million. He refused to say how much he has collected so far.

Tsongas will attend at least one fund-raiser a day for the next two weeks, aides said. He will be soliciting anywhere from $250 to $1,000 from donors at gatherings in New York, California, New Jersey, Pennsylvania and Massachusetts.

Tsongas is hoping fellow Greek-Americans will give generously as they did for former Gov. Michael Dukakis's campaign in 1988, Rizzo said.