Sandra James, whose 6-year-old son and a friend died in a fire at her Reston apartment Monday while she was at work, had only recently taken the part-time job after she learned that the child care she had provided in her home was prohibited under condominium rules, neighbors said yesterday.

"I feel so guilty I could die," Jerris Davis, one of the neighbors, said yesterday. "I {had} said: 'Sandra, I don't want to say anything that will make you upset, but if they see you baby-sitting they're going to make you move.' "

Fire officials said yesterday that the fire that killed Jermaine James and Amanda L. Croson, both age 6, was accidental. Investigators were still sifting through the rubble at the 11633 Stoneview Sq. apartment at Shadowood Condominiums in the effort to determine the cause. No charges have been filed.

Jermaine's 8-year-old sister Tina had been left to supervise him and escaped the fire unharmed, sources said.

The Croson family could not be reached yesterday for comment. According to friends, Larry Barber, a painter, was the father of Sandra James' two children, and he could not be reached yesterday.

James, 25, who returned to her gutted third-floor apartment briefly yesterday, declined to discuss the events preceding the fire, and it was not known what efforts she may have made to find someone to care for her son and daughter while she was at work.

However, local officials and child care advocates said yesterday that the deaths are tragic evidence of a growing problem of children being left alone to care for themselves, often because their working parents cannot afford child care.

Davis and Shannon Hancock, who live in the apartment below James', said yesterday that they noticed recently that Sandra James was taking care of Jermaine and Tina as well as several other children. Worried that she would get evicted, they said, they told her about the condominium's prohibition.

"When I told Sandra this, she looked really stricken. She said, 'I didn't know there was a problem,' " said Davis.

Davis and Hancock said the issue came to a head during a bitter condominium association meeting in February, during which another resident was ordered to stop providing home day care services. Neighbors said they believed that James had stopped providing child care in her home.

The issue has been the subject of litigation in Fairfax and Montgomery counties. In both cases, day care providers lost their attempts to get a judge to overrule condominium bylaws against their operations. The Fairfax case is under appeal.

On Sept. 26, James took the part-time housekeeping job at the Comfort Inn in Herndon, said general manager Diane Edwards. During her short time on the job, Edwards said, James has been an "excellent" worker who often talked about her two children.

"I think it's terrible," Hancock said of the condominium's rule prohibiting day care. "I feel that if she had been up there baby-sitting . . . those kids would be alive."

While condominium officials sympathized yesterday, they said they have to protect the rights of residents in the other 449 units.

Day care services "impact on the common elements," said Carol Bauer, assistant community manager.

"We don't allow businesses in here," said Lou Goddard, vice president of the condominium association. " . . . We're not singling out day care, we're singling out businesses. Period."

Goddard was busy yesterday setting up funds for the families of the victims.

"I don't like having a bunch of kids living next door to me, but they've got to be somewhere," said Mike Herr, who lives next door to the James apartment and manages the Kinney shoe store in Herndon. "Obviously, if someone would have been home watching those kids, two wouldn't be dead and the place wouldn't be burned down."

Although Herr purchased his condominium only two months ago, he said he had noticed 8-year-old Tina James letting herself and her brother in after school with a key.

"A lot of our time is spent on this type of problem," said Tom Hamblen, a supervisor for child protective services in Fairfax County's Department of Social Services. The county had 217 substantiated cases of children who did not have what was considered proper supervision in the past fiscal year, and there are probably many instances that go unreported, Hamblen said.

The agency has established unofficial guidelines that children age 6 and younger should not be left alone, children 7 to 9 should not be alone for extended periods, and baby sitters should be at least 12 to care for children 4 or older.

A recent study found that of 7,200 Reston children between 5 and 14, about 5,000 need child care, but there were only 453 slots available at private day care centers and at school-based programs. It was unknown how many care for themselves.

Nationally, a Census Bureau survey conducted in 1984 and 1985 found that 488,000 children aged 5 to 14, or about 2.7 percent of that age group, cared for themselves when their parents worked.

The county and the state have programs to subsidize child care for low-income families, but these have long waiting lists. Fairfax County spends about $2 million a year on about 900 full-time day care slots at 20 facilities.

Also, the county runs before- and after-school programs for kindergarten to sixth grade. With 2,200 slots at 64 elementary schools in the county, more than 800 children are on the waiting list, according to the Fairfax Office for Children. While full fees for both before- and after-school care reach $173 a month, at the lowest income level the fee is as low as $3.50 a month.

The schools that Jermaine James and Amanda Croson attended, Terraset and Navy Elementary, respectively, are not among those that have the school-based program, officials said. Even where the program exists, it does not operate on some school holidays, such as Monday's Columbus Day break.

Two years ago the state legislature started a $1.5 million program for subsidizing home day care services for some low-income families; the money was gone quickly.

James A. Payne, chairman of the State Board of Social Services, wrote to local social service agencies in September, asking them to push for more funding and saying that day care services otherwise would have to end for some of Virginia's neediest families.

"Many families affected will have to resort to total welfare dependency . . . or face the choice of leaving their young children unsupervised or in substandard care," he said.