School and health officials in Virginia and Maryland have begun mass immunization programs in an attempt to stop a measles epidemic in the Washington metropolitan area.

More than 350 cases of rubeola or red measles have been reported in the area, and investigators say the majority of victims have been children immunized too early, or with ineffective vaccine.

In the latest outbreak, Howard County, Md., health officials notified 7,500 high school students yesterday that they face suspension by May 18 unless they can show proof of a valid measles immunization or agree to be immunized immediately. Six cases of rubeola, which can lead to pneumonia and to encephalitis, were confirmed Monday at Howard High School, just outside Columbia.

Since the beginning of the year, 300 cases have been reported in Fairfax County, six in Alexandria, 41 in Arlington, 14 in Prince George's, none in the District of Columbia, and a "minimal" number in Montgomery County, according to officials.

The cases being reported are rubeola or red measles rather than rubella or German measles. While rubella can be extremely dangerous to a fetus in the early months of pregnancy, it is not considered serious to children and men and most victims recover in one to three days.

Rubeola, however, can lead to encephalitis, which, with its high fever, can cause permanent brain damage and even death. Additionally, complications can result in a loss of hearing and impaired vision and patients often are kept in darkened rooms and encouraged not to read.

Once one of the leading childhood diseases - with as many as 400,000 cases and 450 deaths a year - the incidence of measles has been curbed dramatically since the mid 1960s when vaccines were discovered and immunization programs begun. Most states, including Maryland, Virginia and the District of Columbia, now require measles immunization as a condition of school attendance.

In the early years of the immunization programs, the vaccines often were given in the first 12 months of life. It since has been discovered that at this early stage, a child is still protected by its mother's antibodies, rendering the vaccine ineffective.

Additionally, officials said, it has been found that some of the earlier vaccines did not confer permanent immunity. Both categories account for the majority of cases in the current epidemic, officials said. An epidemic is defined as the incidence of three or more cases at a single place or institution, they said.

According to officials at the Center for Disease Control in Atlanta, 27,360 cases of measles were reported nationwide between Jan. 1 and April 30 of this year, an increase of 60 per cent over 1976.

In the Washington arta, the measles outbreaks have been spread unevenly with some sections being particularly hard hit while others appear to be unscathed.

In the District of Columbia - where more than 100,000 school children were immunized against measles in the early 1970s - there have been no reported cases.

Arlington has confirmed 41 cases as of yesterday, with the majority of them being confined to two schools, Kenmore Junior High School and Long Branch Elementary School. More than 300 children were immunized at a special immunization program Wednesday night at Kenmore and Arlington health officials announced yesterday that the County health office at 1800 N. Edisen will open on Fridays between 3 and 4:30 p.m. for measles immunizations.

Additionally, notices have been sent home with all Arlington school children warning that they should be reimmunized if they received the vaccine during the first 12 months of life or if they were inoculated with a vaccine containing a dead virus, now not considered to confer permanent immunity.

In Prince George's County officials said there have been 14 measles cases reported so far this year compared with 16 during the whole of 1976. Three have been in the Bowie community and two at Bowie Senior High School. Officials yesterday said Bowie students would have to show proof of immunization after the age of 12 months with a live vaccine, agree to be re-immunized or be suspended.

The large number of cases in Fairfax has let U.S. health officials to visit local schools to determine why some students immunized against the disease have contracted measles while others have not. Immunization clinics have been held at four schools during the past six weeks, and two more are planned.

Joseph C. Muzyka, Fairfax County's director of health education, said one difficulty has been that many parents do not take measles seriously.

"Some of the parents and some of the adults just don't think it's important enough to worry about," he said. "They think it's just another childhood disease."

Statewide, Virginia has recorded more than 900 measles cases this year while in Maryland the number is 290, with about 240 of them being concentrated in the eastern part of Baltimore County. In Maryland, health officials announced yesterday the beginning of a massive immunization drive, not only against measles, but also against polio, diphtheria, whopping cough, mumps and tetanus.