When 64-year-old Alfred H. Thompson saw that workers were about to start digging into his family's burial plot -- a half acre surrounded by a shopping center off Lee Highway in Fairfax -- he stationed himself before them with a sledgehammer.

That act of definance Oct. 8 promptly caused his arrest on a trespassing charge. Yesterday that charge against Thompson, a retired Navy lieutenant commander, was dismissed in Fairfax General District Court when the complainant failed to appear.

The plot at the southest corner of Lee Highway and Nutley Street was the burial ground for the Thompson family as early as 1792, according to Thompson's 30-year-old son, Alfred Jr. The will of Thompson's great grandfather mentioned it as a family cemetery in 1886.

Now, Thompson patrols the land, where only two tombstones remain amid locust and persimmon trees, to prevent encroachments such as that of the workers who claim they have the right to build a storm sewer there.

For six years, Thompson has defended the land against the claims of the Pan American Shopping Center Corp., which recently opened a shopping center around the graveyard.

Thompson maintains that when a cousin sold the land around the cemetery to Pan American in 1973, she stipulated "that the cemetery wasn't part of the deal."

Lawyers for Pan American Took the case to Circuit Court in 1973 arguing that the company owns the plot and has the right to develop it.

Judge Percy Thornton disagreed, citing the will of Thompson's great grandfather Lawson Turner Thompson. The judge ruled that the burying ground was protected by state law and Pan American didn't have the right to develop it.

Despite the victory, Thompson's lawyer, John H. Rust Jr., warned Thompson in a letter last April: "It appears that your family will always be required to keep a careful eye upon the property to prevent this sort of encroachment."

Yesterday, as he patrolled the land, Thompson said: "This is something where my family -- and there are Thompsons all over Virginia -- can come to see a part of their history. But every week I come out here, those workers are pecking away at the land.

"They were cutting at least eight feet into the plot when I put my foot down and got arrested," he said.

The storm sewer the workers were constructing was the project of Pan American, according to Don Hollin, an attorney for Thompson.

Glenn R. Mills, an employe of the Mozel Development Corp., a subsidiary of Pan American, filed the complaint that resulted in Thompson's arrest.

When asked yesterday why he failed to appear in court, Mozel replied, "I thought the court date was Nov. 24."

The sewer construction across the land has been completed, according to Thompson's son Ralph, 30.

Another threat to the burying ground apparently is posed by the Virginia Department of Highways, which said in a letter last March that they "do not agree with the decree of Judge Thornton regarding the limits of this cemetery." D.E. Ogle, an assistant engineer with the department, said in the letter than "we are presently planning to establish the right-of- way line of Route 29/211 adjacent to the cemetery."

Yesterday, Thompson pointed to a marble tombstone on the land, remarking that it is his "great-grandfather's oldest brother, Armistead T. Thompson. He was a Confederate soldier who died in a Union prison camp Nov. 23, 1864." He said there are "at least eight other Thompsons here."

Thompson said he was embarrassed and insulted by his arrest, but plans to continue his vigil on the land.