Representatives of the National Labor Relations Board have accused Scan furniture management of unfairly forcing a new contract on its 170 unionized warehouse and store employes and prolonging a bitter four-month strike at the company's 12 Washington area stores.

The NLRB's Baltimore regional office issued a complaint Tuesday that cites Scan, a consumer-owned cooperative, for imposing a final contract offer for salary and benefits and for subcontracting some furniture delivery jobs when contract negotiations could have continued.

"The decision says what we've been saying all along," said James Lowthers, spokesman for Local 400 of the United Food and Commercial Workers union. "The simple answer to why the strike has been continuing is right here: They pushed us out on the street and never intended to settle . . . . They never intended to bargain, never intended to compromise."

But Scan President Robert Satake said yesterday he believed the decision against the company was in error. He said the hearing would give Scan management a chance to explain why it declared an impasse. Labor law requires the company to bargain in good faith until it reaches a genuine impasse, at which point it can impose its final contract offer.

"The hearing will be an opportunity to clear our good name," Satake said. "Scan presented a final contract offer which the union just flatly rejected."

The allegation by the board's regional office will be reviewed in an administrative hearing in Washington in a few months. The complaint comes three weeks after the same regional office issued a complaint against the union, charging that its members caused property damage and threatened workers who crossed picket lines. That complaint has been set for review in December, a board spokesmen said yesterday.

About 170 union members began walking picket lines May 4 after six weeks of unsuccessful bargaining over separate two-year contracts for warehouse and store employes.

Union members described the NLRB decision yesterday as an encouraging one that might help end the dispute between the workers and the Greenbelt Cooperative Inc., a 45-year-old consumer-owned enterprise that directs Scan operations. Scan is the retailing division for the 110-member cooperative, the largest consumer cooperative on the East Coast.

"I've been walking a picket line for seven days a week for four months," said Tom Teates, shop steward at the Aspen Hill store and a 12-year sales employe. "I would say I've lost about $10,000 in pay from this . . . . It's very strange. There's been no attempt by the company to discuss anything."

Union representatives said the company's demands include pay freezes, a cut in sick-leave pay, the elimination of a sales commission plan that shares all commissions equally among employes, and a loss in seniority as a basis for awarding overtime hours.

Company representatives, citing increased competition, said the money that employes wanted in raises would have to be used instead to pay for improvements in health benefits. Other company proposals are aimed at reducing waste and adding incentives to increase sales, such as basing commissions on productivity, they said.

Union representatives said yesterday they had compiled information from Scan records that show furniture sales have dropped between 35 to 75 percent since the strike began. Company representatives said yesterday sales have dropped 10 to 12 percent.

Scan, which had profits of $600,000 in 1984 and $1 millon in 1985, suffered a $400,000 loss last year because of competition from other retailers of Scandinavian furniture, such as Scandinavian Gallery and Marlo Furniture, company spokesmen said.