The dump trucks laden with sludge trek to Dickerson every day from the Blue Plains sewage treatment plant in Southwest Washington, arriving at the 273-acre site in upper Montgomery County where Edwin and Julia Matthews once raised dairy cows and grew corn.

It was almost two years ago that the Montgomery government paid the Matthews $1.5 million for the farmland and entered into an unprecedented agreement with a vocal citizens group to open the temporary $7-million plant and begin mixing sludge with wood chips to create fertilizer.

Two years later, the facility, set in the shadow of Sugarloaf Mountain, has become a national model--and proof of the once-questioned claim that there is a market for processed sludge-turned-fertilizer. In fact, the Dickerson facility has become so successful that buyers from as far away as Saudi Arabia have traveled to Dickerson to buy $20 bags of fertilizer.

But despite the success of the plant, county officials say it will stop accepting sludge Dec. 1. The Dickerson plant's sludge, up to 400 tons daily, will be taken over by a new, more advanced sludge composting facility known as "Site II," which will open in February near Calverton, about a mile from the Prince George's County line. In the meantime, the sludge will go to Virginia under a private contract.

The plant's scheduled closing represents a victory for area citizens, who have long felt isolated and politically powerless compared to central Montgomery residents around Bethesda, Potomac and Silver Spring. But the citizens' victory celebration is muted because of concern over the fate of the plant's 42 employes, and out of fear that even if the plant is closed, it may eventually be reopened.

"We wanted to make sure the sludge was out of Dickerson," said Steven P. Quarles, president of the Sugarloaf Citizens' Association. "But I am of two minds about the closing on Dec. 1. It means those employes will get their notices shortly before Christmas, with only a hope of being rehired at the new facility."

Quarles said the other major concern is "we want to make sure that if it is closed, it stays closed."

The plant workers, all up-county residents, are employed by the Maryland Environmental Service, which operates the Dickerson plant. The Washington Suburban Sanitary Commission will operate the new plant, and initially said tight union rules would prohibit hiring the Dickerson employes.

But after a meeting Thursday between County Executive Charles W. Gilchrist and WSSC officials, the commission agreed to try to hire the Dickerson workers. "The WSSC will make every effort to employ all the people employed at Dickerson who want to work at Calverton," said WSSC commissioner Leonard H. Tietelbaum. "We should be able to take most, if not all."

Dickerson was designed as a temporary facility to handle the Montgomery and Prince George's portion of sludge generated at the regional Blue Plains plant. The Dickerson plant was supposed to be replaced by the permanent facility, but Quarles said up-county residents fear the new, highly automated plant will not work properly, will be forced to close, or will be unable to handle all the sludge.

"If there's a healthy paranoia in our community," he said, "it's to make sure those trucks don't get halfway down the road then turn around and come back."

Alexander J. Greene, a special assistant to Gilchrist, said the county is committed to closing the facility to fulfill its unusual agreement with the Sugarloaf Citizens' Association. In 1981, Gilchrist called that agreement an "unprecedented" example of citizen-government cooperation in a county where well-funded citizen groups have often done bitter battle with their government, particularly over what to do with garbage and waste.

The Sugarloaf citizens opposed the plant's opening two years ago for fear it would smell and contaminate Dickerson's well water. But after the unusual mediation with the county, they agreed to drop their court suit and not to oppose the facility's health permit. In return, the county promised to close the Dickerson plant when the permanent composting plant opened, which was originally scheduled for Sept. 1.

That date was postponed because of engineering delays at the new plant. And despite the county's assurances, some Dickerson residents are still suspicious that the delay could mean Gilchrist is reneging on his promise. Not true, said county officials.

"Dickerson is being closed," said Edmond F. Rovner, special assistant to Gilchrist. "We said we were going to close it and we will close it."

But many residents still are skeptical. So worried are they that the county is stalling that a public hearing last week, called to consider new uses for the site, got bogged down in discussion of whether the plant would actually close.

After that meeting, the citizens presented the county with 1,253 up-county resident signatures on petitions demanding the plant be shut down.

"I'll believe it when I see it," said Sally Dilonardo, a Dickerson resident for almost 30 years, about the scheduled closing. "We have gotten a little bit cynical."