Magruder's Grocers, the target of bitter labor organizing drives for more than a decade, has voluntarily accepted union representation after a majority of its 900 employes signed union authorization cards at its eight Washington-area markets, company and union officials said yesterday.

The voluntary acceptance of a union at the growing 109-year-old grocery chain was unusual because it came without a government-supervised election.

It follows recent private meetings at which the United Food and Commercial Workers union threatened to set up picket lines and mount a major campaign to publicize the company's wage and benefit levels, which are lower than most unionized competitors, according to union sources.

"We have agreed," said Mark Polsky, president of the Rockville-based chain, which is known for its variety of specialty foods and its discount prices.

Polsky declined further comment, except to confirm that the company will shortly begin negotiating a first contract with the Landover-based UFCW Local 400.

Local 400, whose 30,000 members make it the largest and wealthiest local union in the area, told company officials last December they would "put everything they had" into a publicity campaign about Magruder's, the largest nonunion supermarket chain in the area, according to an AFL-CIO official familiar with the private meetings of union and company officials.

Most union drives result in contested elections supervised by the National Labor Relations Board, but the 1-million-member UFCW, one of the nation's fastest-growing unions, has frequently attempted to bypass the lengthy NLRB procedures and win voluntary recognition by gaining strong majority support before confronting employers.

Instead of contesting the union claim, Magruder's agreed to a "card check," which was held last Monday, and agreed to recognize the union after validating the signatures of a majority of employes on cards specifying that they wanted a union.

Magruder's had strongly resisted previous organizing attempts by Local 400, which represents Giant, Safeway, Food Town and other groceries. Magruder's officials had said they could not afford to pay the higher wages and benefits of the larger food chains.

Wage and benefit levels vary at Magruder's, but the majority of employes earn between $4 and $5 per hour, said C. James Lowthers, assistant to Local 400 president Thomas McNutt. Union contracts at Giant and Safeway have starting hourly salaries of $5, but rise to $9.35 per hour in the third year. Veteran unionized food clerks earn about $12 hourly.

There are two Magruder's stores in Rockville and one each in Annapolis, Bowie, Vienna, Annandale, Fairfax City and the District.