The way Joe Mondichak sees it, he and three buddies who work for Giant Food were just looking for a few beers when they walked into the Shapiro's Food Town in Northeast Washington one night after work.

There was a picket line outside the store and, though he's a union member, Mondichak ignored it--until one of the men on the line spotted a Giant insignia and, as Joe tells it, "started hassling us."

"We weren't trying to cause any trouble, we just wanted to grab a couple of six packs, but they started giving us a hard time. I spent a year in Vietnam and I figure I've got the right to buy my beer where I want to."

The harsh words on the picket line escalated into a union disciplinary action against Mondichak after the pickets noted his license number and tracked him down. Now Mondichak faces a hearing Tuesday night on charges that he violated union policy by crossing a picket line set up by his own union.

Joe'll probably get off with a slap on the wrist, but the decision to press the case shows the determination of Local 400 of the United Food and Commercial Workers to keep nonunion food stores out of Washington.

More than 90 percent of the supermarket sales in the Washington area are rung up by Local 400 members, who face the strongest threat ever to the union contracts that make them some of the best paid workers in the food industry.

"D.C. is the only place left on the entire East Coast where the chain contracts haven't been eroded by nonunion operators," says Local 400 President Thomas McNutt.

There is particular pressure on the unions now because the recession is forcing the intensely competitive supermarket industry through yet another shakeout.

Pantry Pride bit the bankruptcy bullet, then bit the dust, and hundreds of union jobs died with it.

Acme Markets warned its unions earlier this year that it could not survive without wage concessions; then, after the unions caved in, pulled out of the East anyway. Acme announced a couple of weeks ago that it was closing all its Baltimore stores and now, McNutt says, the company plans to shutter its last four stores in the Washington area on June 5, laying off about 90 Local 400 members.

Grand Union appears to have successfully outflanked the other big chains with its high-volume, low-price Basics discount food stores, but the conventional Grand Unions are hurting. With a solid position on the bottom of the price market, Grand Union reportedly plans to try to skim off some of the top by opening gourmet stores. If that works, Grand Union could swim out of the mainstream.

What's left of the once-Great Atlantic & Pacific Tea Co. lingers on the life-support system of its German owners, the Tengelmann Group, utilizing one "miracle" cure after another to keep alive.

When the Price and Pride joy boys, who were supposed to resurrect A&P, turned out to be more like Dr. Jekyl and Mr. Hyde, they were followed by the "Plus" cure--a plan to transplant to the United States the warehouse format and the name Tengelmann uses in Germany. Plus may be an acronym for some catchy German phrase, but twisting it into Priced Low, U-Save was too much for the customers to comprehend.

The latest A&P panacea was disclosed Friday in Philadelphia. Local politicians and A&P officials said they had found a way to "save" a couple dozen stores and, with them, the jobs of several hundred union members. The stores will be taken over by a new subsidiary formed in partnership with the unions, which will not only give wage and benefit concessions but also invest in the venture.

A&P closed 13 Washington are stores last December and sold seven of their locations, but it is still holding on to six more stores. Union officials are watching closely to see what happens to them.

When A&P, Pantry Pride, Acme and others falter, close stores and fold, local independents often move in. They buy the fixtures and leases at going-out-of-business-sale prices and set up shop without union contracts or with lower pay scales.

In Baltimore, where the erosion has been as bad as any place on the East Coast, one independent is paying 60 percent of the old union scale for clerks and 75 percent of union meatcutters' wages.

The Baltimore backsliding is what has McNutt worried and is why Joe Mondichak is in trouble for crossing a Local 400 picket line. Shapiro's came from Baltimore.

"Shapiro's probably isn't one-tenth of 1 percent of the Washington market," McNutt acknowledges, but his members have been picketing the store for three solid months because much more than a few union jobs is at stake.

McNutt says the stores that are faltering in today's environment and demanding concessions are, in effect, telling the unions, "they can't do it as a merchant, so we have to give them a labor rate advantage. I can't justify to Safeway and Giant giving anyone else a labor rate advantage."