Two Montgomery County high school students and a third suspect were arrested yesterday on charges that they broke into a Potomac home Monday and sexually assaulted a 19-year-old woman at gunpoint in her basement bedroom.

Montgomery police said they were searching for a fourth suspect last night but did not release his name. Police said the woman knew at least one of her attackers. Court documents state that one suspect -- it is unclear which -- asked the three others to come with him to the woman's home.

Two of the suspects are seniors at Montgomery's Winston Churchill High School, officials said. The third suspect, 16, lives in Upper Marlboro. Prince George's County officials would not say whether he attends a county school.

The woman told police that the teenagers, wearing ski masks and bandannas, attacked her about 3 a.m. while her parents and younger sister slept upstairs in their home on Falls Chapel Way. She said one of them showed her a gun and demanded that she undress and stay quiet before two of them raped her and three forced her to perform oral sex, according to court documents. They then stole computers and other items, the documents say.

The two Churchill seniors were identified as Schmouree L. Fordyce-Williams, 19, of the 12000 block of Gatewater Drive in Potomac, and Kevin Curtiss Croker, 17, of the 8800 block of Watts Mine Terrace in Potomac.

Fordyce-Williams was being held last night in lieu of $250,000 bail on charges of first-degree rape, first-degree sex offense, first-degree burglary and using a handgun in a violent felony. Croker was charged as an adult with first-degree rape, first-degree burglary and using a handgun in a felony. He was being held last night without bond.

Chris Benbow, 16, of the 4900 block of King Patrick Way in Upper Marlboro, was being held last night in lieu of $250,000 bail. He was charged as an adult with first-degree rape and first-degree burglary, authorities said.

A message left at Croker's home was not returned yesterday. A woman who answered the phone at Benbow's home declined to comment.

Fordyce-Williams's mother, Andrea Fordyce, 43, said she drove her son to the police station Wednesday night for questioning.

On the car ride, she said, he told her he was innocent. Four hours later, she said, a police officer told her that her son had admitted to the burglary and would be arrested.

"My child is a follower," said Fordyce, a Montgomery school bus driver. "I've always been afraid of this. . . . This is not the son I raised."

Fordyce-Williams's older sister, Schmeara Spears, 22, said the victim had thrown a party at her home the night before the attack. Spears said her brother told her one of the suspects took the woman's key from under her welcome mat and used it to get in the following night.

Police said Fordyce-Williams told them during questioning Wednesday night that one of the other suspects came to his home about 2 a.m. Monday and asked him and two other acquaintances who were at his house to go with him to the woman's home.

An examination at Shady Grove Adventist Hospital showed that the woman had been raped, police said.

Staff writers Rebecca Dana and Nancy Trejos and staff researcher Bobbye Pratt contributed to this report.