Four years after President Reagan intervened to arrange nursing care for a chronically ill Gaithersburg boy, the boy's health insurance provider has decided to reduce the amount of care it is willing to cover.

Don Broom, a 6-year-old who suffers a multitude of ailments stemming from his premature birth, has received 24-hour nursing care at home paid for by a federal employe benefit plan at Blue Cross/Blue Shield. Normally under the insurance plan, only 90 days of nursing care per year is provided. But in 1983, when Reagan learned about the boy's chronic heart and lung problems, he arranged a waiver of the contract so that the child could receive additional help.

Last month, Blue Cross/Blue Shield reduced the round-the-clock care to 16 hours per day during the week and 12 hours per day on the weekend. According to the plan's claims services director Robert A. Flohr, the decision to reduce the hours was "based on a medical evaluation of the patient's needs." Flohr said the child's doctor said he needed to be monitored, but "gave no specific indication as to the number of {nursing care} hours this child requires."

"It's really unfair," said the child's mother, Geraldine Broom. She said yesterday that she believes 24-hour care should continue because, although Don has stabilized over the last few years, "his medical condition has not changed." She said he still requires the same equipment and medications that he needed when he was released by the hospital four years ago.

Broom said the nurses cost $17.50 an hour, or $1,820 a week under the newly arranged hours. The insurer also pays for the compressor and oxygen that keeps the boy breathing, and Medicaid pays for the child's medication, Broom said.

Broom, 26, is separated from her husband, a power plant worker at the National Institutes of Health. She said they cannot afford to pay for the additional nursing care and there are no family members in the area to help them.

Broom, a former waitress who graduated from Montgomery College nursing school last week, said she wants to get a job "to support my son," but feels she cannot do so without round-the-clock nursing help.

Broom contacted the local news media and President Reagan last week seeking help.

Yesterday, a White House spokesman said officials there are not getting involved in the family's dispute with the insurance plan. However, according to the spokesman, Ben Jarrett, the Office of Personnel Management, which oversees the health plan for federal employes, may reconsider the case if another physician refutes the Blue Cross/Blue Shield decision to cut back on nursing hours.

Joanne Kausman, director of the Coordinating Center for Home and Community Care, a federal government contractor that assesses needs of children such as Don, told Blue Cross/Blue Shield that children with similar problems receive about 12.8 hours of home care per day paid for by other insurers.

"There are others in worse shape who are doing it with less professional help," Kausman said yesterday. She said family members often make up the difference by learning to perform tasks themselves.

Usually, home care is provided as a less expensive and more humane option to hospitalization, Kausman said, but she added that Don's problems are so severe it might be less expensive to care for him in an institution. A bed at the Hospital for Sick Children in the District, for example, would cost $305 a day, Kausman said. "That, of course, is not what we want" for Don, she said.

Geri Broom said she has no intention of putting her son in a hospital. He was born in 1980 weighing 1 1/2 pounds and lived at Children's Hospital for two years, Broom said. The boy, who is albino, was "nearly a vegetable" when she brought him home, she said.

Now, the chubby, giggling child attends a special school two hours a day and is learning to walk and talk depite his mental, visual and hearing handicaps.

Don's daytime nurse of four years, Emmy Bonnell, also is concerned with the cutback in care hours. She said a nurse can tell the signs of impending heart or lung distress and knows how to handle his seizures. "A regular person can't do that," Bonnell said.