Using direct-mail, catchy ads, a "turkeybusters" radio jingle and a $1 cash rebate offer, the Washington area's largest union is waging a Thanksgiving multimedia attack aimed at pressuring the Marval Poultry Co. to end a strike at the world's largest turkey plant in Harrisonburg, Va.

"We are having some impact and we are going to keep the pressure on through the holidays . . . as long as it takes," said Thomas McNutt, president of the 30,000-member Local 400, United Food and Commercial Workers, based in Landover.

The union is spending well over $100,000 to promote the AFL-CIO-supported boycott of Marval, where roughly half the 900 workers walked out June 2 in the first strike in the Shenandoah Valley's $250 million-a-year turkey industry.

Using AFL-CIO mailing lists, the union has sent rebate coupons to about 75,000 Washington-area union members, offering $1 refunds to those who buy brands of turkey other than Marval.

The union has also mailed 400,000 leaflets to Maryland and Virginia families urging them to boycott Marval's Manor House, Esskay and other brands of turkey products carrying Marval's P-18 Department of Agriculture code.

Officials of Rocco Enterprises, Marval's parent company, have said that the union boycott has had only minimal impact. Company officials were not available for comment yesterday, but Robert A. Wolfe has said in response to union charges of unfair labor practices that Marval's actions have been investigated by the National Labor Relations Board and found to be lawful.

The dispute arose when the two sides were unable to negotiate a new contract for the employes, who earn an average of $5.50 per hour. Rocco sought to include a new contract provision to make it easier for workers to quit the union, a demand UFCW strongly resisted. The union contended Marval imposed harsh working conditions by speeding up the turkey-killing lines and imposing stringent work rules.