D.C. police yesterday charged a third man in the slaying of a Southeast Washington grandmother who was struck by two stray bullets while protecting children from a gun battle behind her home.

London Marquis Ford, 18, of the 5100 block of Call Place SE, was charged with murder while armed, police said. He was the second man from the Marshall Heights neighborhood charged in the death of Helen Foster-El. Jimmy J. Shelton, 18, of the 5100 block of Hanna Place SE, is also charged with murder in the case. The charges against Derrick Terell Jackson, 19, of the unit block of Hanover Place NW, who had been charged with murder, were downgraded yesterday to carrying a pistol without a license.

All three were denied bond last night during a brief appearance in D.C. Superior Court. Police said early this morning they had identified and were searching for a fourth suspect, a 21-year-old man already wanted on an outstanding bench warrant.

Charging documents released after the hearing said investigators believe the gunfight arose from an argument that took place about an hour earlier behind the 100 block of 56th Place SE. Witnesses told police that a man with hair braided in cornrows struck another man in the head with a handgun; the man with the cornrows returned about an hour later with another armed man, according to the court documents.

"The . . . ones who had been involved in the original argument once again began to argue," the affidavit said. "A gun battle then erupted."

The affidavit said witnesses identified Ford as the man with cornrow braids and Shelton as the armed man who accompanied him. One of the witnesses told police that the man with cornrows opened fire and that "other individuals" returned fire across an alley.

Police said Ford corroborated many of the witnesses' accounts, but Ford said the man he had been arguing with was toting a TEC-9 9mm semiautomatic weapon when he returned. Shelton and Ford made no mention of Shelton carrying a weapon in the affidavit. Ford acknowledged that he was carrying a .38-caliber handgun and that he fired the weapon.

"When asked where did he shoot, Ford stated, 'Not even for sure, I just tried to get away,' " the affidavit said.

Shelton told police that he and Ford were approached by a group of armed men. He said Ford pulled out his gun and returned fire when the other men shot at him.

D.C. police said in the affidavit that evidence technicians recovered 19 shell casings, all of them from 9mm weapons, and that all but two of those casings were fired from the same weapon. The technicians recovered three spent bullets--two from the victim's body and clothing and one from a neighbor's home--fired from a 9mm weapon.

Yesterday, Shelton's father, Jimmy J. Green Jr., said a dispute over payment for an auto collision was the catalyst for the gun battle that resulted in Foster-El's death.

Green said his son told him that he drove a friend in Shelton's gray Chevrolet Caprice to 56th Place SE to collect cash owed to the friend because of a crash that damaged the friend's car. Shelton told him that the man not only refused to pay but also pulled out a gun and started firing, Green said. The friend then pulled out a gun and returned fire while Shelton first dived for cover and then drove away, Green said.

Green did not identify his son's friend. Foster-El was hit in the back and in the leg by the cross-fire.

"If you don't know what's going on, you can't be an accessory," Green said of his son, who he said attended Eastern High School. "He went straight, man."

It could not be determined last night whether investigators have heard Green's version of events.

Green said he had warned his son about his group of friends and advised Shelton to turn himself in Tuesday night.

"I said, 'If you didn't do anything wrong, go turn yourself in,' " Green said. "That's what he did."

Green, 37, said his son had been put on probation this year for 12 months for possessing a 9mm Glock handgun but had not not been in trouble since.

Nancy Salmon, a cousin of Ford, said Ford graduated from H.D. Woodson High School on June 14. Salmon, who lives in the same apartment building as Ford, said she didn't think Ford had been in trouble with the law before.

The family "is taking it pretty bad," Salmon said. "I feel bad about it. He just graduated from high school, and we were very proud of him. It was kind of hard for him, but he did [graduate]. So we all went to his graduation and then took him out to dinner. He grew up without a father, and we just wanted him to know that we are proud of him."

Foster-El's family and friends made funeral arrangements yesterday and expressed relief that arrests have been made. Police sources said yesterday they expect to charge one or two more people in the case.

Evelyn M. Brown, who sang in the women's choir at Open Door Baptist Church with Foster-El, said longer-term community police presence is needed.

"This thing is hot and heavy right now, but in three weeks it's going to be history," said Brown, who is also president of the resident council at East Capitol Dwellings, where Foster-El lived. "They need to keep it hot. They need to put a stop to this thing. Police are now walking through the community; they should have been doing this all along. Not just driving through--walking and talking to people in the community."

Foster-El's wake will be at 10 a.m. Monday at Open Door Baptist Church, 136 56th St. SE. The funeral will follow at noon.

Family members plan to take Foster-El's body to Richmond for burial.

The church announced that it had established a Helen Foster-El Memorial Fund and asked that contributions be sent in lieu of flowers to NationsBank or to Open Door Baptist Church.

Metro researcher Bobbye Pratt contributed to this report.

CAPTION: Defendants Derrick Terell Jackson, Jimmy J. Shelton and London Marquis Ford, right, appear at a hearing in D.C. Superior Court. The charges against Jackson were downgraded to unlicensed carrying of a pistol.