At 9:30 this morning, Agnes Blackstone is scheduled to appear at a preliminary hearing in Circuit Court here on a charge of assault with an intent to kill. Blackistone, 64, is accused of pointing a loaded rifle at 15-year-old neighbor's son after the boy cut across her property without permission.

At first glance, it was one of those incidents that occur sometimes in rural areas when neighbors don't see eye to eye and start quarreling.

To blacks in this part of southern Maryland, however, Agnes Blackistone's case involves more than just quarreling neighbors. To them it is a case that symbolizes the way things work in St. Mary's County if a person happens to be poor and black.

Agnes Blackistone is a rarity among St. Mary's County's 20,000 blacks because she owns her own home and nearlyan acre of land around it. Although exact figures are unavailable, real estate salesmen in the county estimate that blacks own only about 5 percent of the county's land and houses, even though they comprise 40 percent of the population.

According to Blackistone, a neighbor, William Pulliam, who is white, has tried to intimidate her into selling herproperty. On the night of Aug. 31, she says she grabbed a rifle "for protection" and ran outside to tell Pulliam's son to get off her property.

Blackistone has filed a countersuit against Pulliam charging trespassing, and a false arrest suit against the St. Mary's County sheriff charging that she was never shown a warrant when she was arrested.

Meanwhile, black leaders in the county have asked the Southern Christian Leadership Conference to investigate, and are preparing to ask the Justice Department to intervene.

The SCLC's North Atlantic regional vice president, Henry Silva, said he hasn't "seen one like this since the old days in the South. It's the age- old problem of a white man feeling he can do what he wants to do just because his adversary is black."

Blackistone, a gruff, chain-smoking retired laundry worker who never got past the seventh grade and who says she never earned more than $2.10 an hour, is "prepared to fight this wherever it takes me.

"I had no intention of doing nothig to the kid. But I have no intention of letting them use me, either," she said.

A lifelong resident of the county, Blackistone had never been arrested before last Sunday, according to sheriff's records.

"But if Martin Luther King went to jail, I guess I can, too," she said.

Pulliam, who is full or part owner of two gas stations and a grocery in southern St. Mary's County, refused to be interviewed or photographed. So did his son and his attorney, John Weiner. "It'll all come out in court," said Pulliam's wife, Patricia, before she hung up the phone on a reporter last week.

The Blackistone-Pulliam feud has not become a cause celebre in Sr. Mary's County because few know about the last 10 years. In addition, ered it, and several top county officials knew nothing about it last week.

Part of the reason, one official suggested, is the size and nature of the county. It spans almost 50 miles of gently rolling farm land, from the Charles County line to Chesapeake Bay.Leonardtown, near the center of the county, is 57 miles from the White House.

Most of the county's 55,000 residents support themselves as farmers although 20,000 are either employees of Patuxent Naval Air Station In Lexington Park or their dependents. Houses in St. Mary's are almost several hundred yards apart. News can travel slowly.

Blackistone, a divorcee who lives alone, has owned her home -- a one-story, wood-frame bungalow about six miles south of Lexington Park -- for 18 years. William Pulliam has owned the lot immediately to the east for about 10 years. wIn addition, Pulliam's Grocery, which William Pulliam also owns, sits directly across Mattapany Road from Blackstone's property.

"We always got along good," Blackstone said of Pulliam. "I traded at his store and all. I think the trouble really started last February."

That was when Pulliam bought the one-acre parcel that sits behind the Blackistone property. The previous owners had been an elderly black couple "who were sick all the time and had to get to the doctor. So I let them use the road through my property to get to the main road," Blackistone said.

However, Blackistone never put her permission in writing, and according to her attorney, Patrick Hudson, county deed records show that no such permission has ever been granted in writing by any owner of the Blackistone property.

"I feel Mrs. Blackistone has an absolute right not to let anyone use that road," Hudson said. He pointed out that there are two other roads leading from the one-acre lot behind theBlackstone property to nearby Md. Rte. 235. "Pulliam could easily use them," Hudson said.

Early in August, Hudson advised Blackstone to post "No Trespassing" signs and to blockade the dirt road if she didn't want Pulliam to use it.

Pulliam responded by blockading Blackstone's blockade -- hemming in her Ford with a Chevrolet van at one end and a Mercury Capri at the other. "He told her that if he couldn't get in, she couldn't get out," said Blackistone's daughter, Betty.

Sheriff's deputies were called, and they ordered all three vehicles moved. But later the same day, Blackistone said she saw the same van pulling into the road. "I was afraid," she said, so she grabbed a rifle she keeps for protection" and ran outside. Glenn Pulliam was standing their with a teen-aged cousin, according to court records.

"She asked me was I too young to die," says a sworn statement Glenn Pulliam filled. "I said no. She said she if didn't move the van she would kill me."

Glenn Pulliam did. However, according to Blackstone and several of her neighbors, both Pulliams and the tenants who live on Pulliam's lot behind Blackistones property have continued to use the dirt road ever since.

According to W. Clarke Mattingly, the owner of the county's largest funeral home, Pulliam has amassed perhaps 400 acres of St. Mary's County property in recent years, mainly by buying small lots from poor blacks.

Pulliam has bought several of the lots from Mattingly, which the 60-year-old funeral director had accepted as payment for funerals he conducted, Mattingly said.

Mattingly came to own the one acre behind Agnes Blackistone's property in similar fashion.

Blackistone, meanwhile, thinks Pulliam's main aim for the last six months has been "to intimidate me into selling this house to him. He's got me surrounded on three sides already, but that's not good enough for him, I guess."

Will she sell? "I'll die here, mister," she said. "The other blacks here in the county want me to give it up, but it's gone too far for that."