DC Mayor Adrian M. Fenty fired six child welfare workers Sunday, saying they "just didn't do their job" in the case of four girls who had not been seen for months before their decomposing bodies were found at home last week after their mother calmly answered the door.

The dismissals were delivered about 10 p.m. Sunday to the homes of two social workers, two managers and two phone operators who work at the Child and Family Services Agency, union officials said. Fenty said at least two other employees might be let go as the investigation progresses.

Fenty's firm reaction marked the first time the mayor, who pledged to create a more responsive, accountable government, has used mass firings to emphasize to city employees and the public that he will act swiftly.

The case of the four girls, ages 5, 6, 11 and 16, is spurring policy changes in the long-troubled city agency responsible for the welfare of abused and neglected children. Their bodies were discovered when U.S. marshals served a routine eviction notice to their mother, Banita Jacks, who had been living with the corpses in a rowhouse on Sixth Street SE. Jacks, 33, has been arrested and charged with killing her children.

The girls were killed sometime in late spring or summer, authorities believe. But they were alive when a school social worker, with growing alarm, tried to get child welfare workers to look in on the family.

At a news conference yesterday, Fenty (D) played two phone calls from the increasingly frustrated Booker T. Washington Public Charter School social worker, who might have been one of the last people to see the girls alive.

"From what I could see, the home did not appear clean," the social worker, Kathy Lopes, said in a call to police April 30. "The children did not appear clean, and it seems that the mother is suffering from some mental illness and she is holding all of the children in the home hostage."

Lopes first visited the Jacks home April 27, after Brittany Jacks, 16, missed 33 days of school and no one answered a phone at the house.

"The parent was home. She wouldn't open the door, but we saw young children inside the house," Lopes said to a hotline worker at the city's Child and Family Services Agency. "Her oldest daughter, who is our student, was at home. She wouldn't let us see her."

The operator took the information and reminded Lopes, who was clearly distraught that she could not talk to Brittany, that Jacks did not have to let her inside the home.

When Lopes called again April 30, she talked with a police non-emergency, 311 operator.

"I've been transferred all over. I need someone to go out to a home where I believe abuse and neglect is occurring, and I don't want to be transferred to someone else," Lopes said. "It's an urgent matter. CFSA is pretty much sitting on it, and I would like someone to go to the home and check out the home, 'cause I wasn't allowed in it."

The call underscored the agency's failure to help, said Sharalynn E. Bobo, director of child and family services.

"We deeply regret -- I deeply regret -- our failures in responding effectively and rapidly to this family's need," Bobo said. "The system broke down in this case."

Although a social worker made at least two visits to Jacks's home, in the 4200 block of Sixth Street SE, no one answered the door to the rowhouse either time. Less than three weeks later, Child and Family Services staff members closed the case after receiving an unconfirmed report that the family had moved to Maryland.

Authorities allege that Jacks stopped feeding the girls and at some point fatally stabbed Brittany, who would have turned 17 10 days ago. Tatianna Jacks, 11, N'Kiah Fogle, 6, and Aja Fogle, 5, might have been strangled, according to authorities.

"All the requisite information was available to our people, but the follow-up was never done," Fenty said yesterday. He praised Lopes's efforts to pierce the city bureaucracy as "exceptional" but also said such persistence and dedication ought to be the norm.

"She stands out, really, I think, because so many other people just didn't do their job the way they're supposed to," Fenty said.

Since the case broke Wednesday, Fenty has moved to investigate the government's failure to prevent the deaths and to make public the findings. He said the firings were meant to hold employees accountable and to send a message to other city workers.

His response contrasts with the style of his predecessor, Anthony A. Williams (D), who was not prone to react aggressively in public.

Union officials said Fenty was moving too fast and was making individuals pay the price for a flawed system.

"I don't care if you let 100 people go, it's not going to reverse this tragedy," said Geo T. Johnson, executive director of District Council 20 of the American Federation of State, County and Municipal Employees. "You want to do things like make sure policies and procedures are in place that assure this won't happen again."

He added, "I don't think what happened here was a thorough investigation."

Some civic activists yesterday asked why it took a calamity of this magnitude for Fenty to get tough on the Child and Family Services Agency.

SYLVESTER: "...[T]here is now a bare minimum of competency... what we need to change is the culture of some workers in the agency..."

Kate Sylvester, executive director of DC Action for Children, said the Fenty administration has been receptive to reforms. "The agency has been structurally changed, and some things that had been done badly are changed to where there is now a bare minimum of competency," Sylvester said. ". . . Partly what we need to change is the culture of some workers in the agency."

Marcia Robinson Lowry, executive director of Children's Rights Inc., said the agency has improved since a 1989 court case, LaShawn A. v. Barry, sent the agency into federal receivership for eight years. "This case is not itself a setback," Lowry said of the Jacks case. "But it is really important for the agency to examine its mistakes here."

The mayor said the city will examine and revise its policies in an effort to prevent similar incidents. Fenty said no case in which child neglect or abuse is alleged should be closed before the child is located and "appropriate action taken to ensure that he/she is safe."

In such cases, he said, he wants at least three visits to a last-known address at different times of the day or night. He said that child welfare cases that are deemed "incomplete" will be reviewed and that a system will be created to track home-schooling families.

D.C. Council member Tommy Wells (D-Ward 6) , who chairs the committee that oversees city welfare agencies, said he has scheduled a public hearing for today. He said he wants to determine whether this is "an individual failing or systemic failing."