Four hundred employees of Advent Corporation, who lost their jobs last week when the company shut down its Cambridge stereo and video production plant, will qualify for special federal financial aid for the next year.

Advent executives made the announcement late last week as the workers left the plant on their last day. The company is moving to Portsmouth. N.H., where it plans to hire primarily local workers.

The special dislocation benefits, provided by the federal government under the Trade Readjustment Act--which helps workers laid off because of foreign competition--will pay the former employees up to 90 per cent of their salaries.

"The whole thing was very political," Peter Olney, a leader of the facilities' angy workers, said yesterday. He said foreign competition was probably not behind the government's decision.

"We got it because of all the publicity and attention that the media focused on Advent," he added.

While Olney called the federal help "a good thing--we will take any money we can get," he added that the workers "aren't through with Advent yet."

He said that current plans include a suit with the National Labor Relations Board--charging that Advent left because of union activity, a picket campaign at Advent's new Portsmouth facility, and an attempt to convince workers at the new plant to unionize.

Peter Sprague, Advent president, was unavailable for comment yesterday. He said in late December, when the move, was announced, that the company was leaving "purely for economic reasons."