On the sidewalks in front of Washington's finest restaurants, in the parking lots of the biggest suburban department stores and at the gates of the plants that supply electricity to the whole region, a battle is being waged that could change the future of Washington business.

Picketing and passing out literature, union organizers are seeking and winning converts among workers who traditionally have been lukewarm to organized labor.

In recent weeks, the International Brotherhood of Electrical Workers has won a major victory at Potomac Electric & Power Co. The Retail Clerks International Union has called for an election at Woodward & Lothrop. In addition to its well-known victories at Sans Souci and The Gandy Dancer, the Hotel and Restaurant Workers Union has negotiated contracts at The Jockey Club, Le Bagatelle, Romeo & Juliet and Jour et Nuit.

The three simultaneous but independent organizing drives signal a new phase of union activity in Washington and a new direction for the labor movement.

"There seems to be a movement afoot," said Thomas McNutt, president of the 16,000-member Local 400 of the retail clerks. "There's a lot more activity than I've seen here in some time.

"Service unions are where the growth is coming" in organized labor, added McNutt.

Although it is the headquarters of many of the nation's biggest unions, Washington has never been a union town. Except for the printing trades and the hotel workers, who are 95 percent union-represented in the District of Columbia, most of the city's businesses are not unionized; the biggest unions in the district for years have been independents not affiliated with the AFL-CIO.

Part of the reason for the low level of union activity is that Washington lacks the businesses that have long been the base of American labor organizations-industrial and manufacturing corporations.

But the nation's economy is changing and so is the labor movement. As the old industrial unions lose jobs and momentum, labor organizing leadership is shifting to the service sector of the economy-the business activities that dominate the private job market in the Washington area.

With the new unions are coming new labor tactics. To organize Washington restaurants, union leaders shun the usual National Labor Relations Board petition, election and bargaining proceedure, said Ron Richardson, executive secretary of Local 25 of the Hotel and Restaurant Workers.

Instead the union signs up the workers and goes direct to the management demanding a contract. That demand is backed up by a picket line.

"A strike in Washington can be devastating to a restaurant," Richardson said. "The advantage we have when we set up a picket line is that we can communicate directly with the customers."

Although that tactic has worked for the restaurant workers, retail clerks union organizers have been arrested for trespassing for union activities.

The retail clerks now claim between 16,000 and 17,000 workers in the Washington area compared with 11,000 a decade ago and 6,300 back in 1962, said local president McNutt.

About 11,000 of those members work in supermarkets, virtually all of which are organized in the Washington area. As a result of the strong union. Washington food chains pay some of the highest wages in the supermarket industry, $7.89 an hour for journeymen plus a fringe benefit package worth about $300 a month. Supermarket checkers who now make about $315 for a 40-hour week ($7.87 an hour) were earning $3 to $3.50 an hour a decade ago with few if any fringe benefits, McNutt said.

Local 400 is now asking the National Labor Relations Board to hold the biggest union vote ever scheduled in Washington among the more than 6,000 workers at Woodward & Lothrop. The AFL-CIO clerks union is seeking to replace the Independent Union of Woodward & Lothrop Employes as bargaining agent for the Woodies' workers.

The latest development in that bitter dispute between two unions is a $250,000 lawsuit filed by the Independent Union against Local 400, charging that the AFL-CIO union stole the independent's membership list and is using it to lure away the independent's workers. McNutt insists his organizers are using Woodies' rosters complied three years ago when Local 400 tried and failed to take over at Woodies.

The retail clerks' hopes for success this time were buoyed Thursday by the victory of the AFL-CIO electrical workers union over an independt group at Pepco. Until the election results are crtified by the ULRB, the IBEW cannot begin bargainng for the 3,600 Pepco workers previously represented by the Independet Electric Utility Employes Union.

Besides workers at Pepco and Woodies, employes Washington Gas Light Co. have been represented by an independent union. The challenge to the "company union" at Woodward & Lothrop has brought inquires to the union from workers at Garfinckel, The Hecht Co. and Bloomingdales, clerks union officials say.

Union leaders maintain that the motivation for the current organizing push is coming not from the powerful national labor organizations, but from the Washington workers. That's because "Washington has the highest living costs" in the region represented by the electrical workers union that won at Pepco, said the IBEW's director of organizing, Michael Lucas.

In restaurants, where workers can be fired, literally, at the drop of a tray, job security is as important an issue as money, said restaurant organizer Richardson.

Only about 5 percent of Washington's restaurants have union workers now, he added, and most of them are expensive full-service dinner houses. The more expensive places can afford to pay better and are easier to organize than the chains and fast-food franchises, Richardson admitted.

The biggest test of the hotel and restaurant workers union will come when Marriott Copr. opens two new Washington hotels, one adjacent to Blackie's House of Beef, the other on Pennsylvania Avenue across from the Willard Hotel. None of the local workers in the Marriott food and lodging empire are union members at present. CAPTION: Picture, Pickets at San Souci last year: communicating with customers. By Charles Del Vecchio-The Washington Post