Washington-area children are starting school this year with record levels of protection against polio and the once-common but potentially dangerous childhood diseases, government health statistics indicate.

As a two-year nationwide campaign nears its end, the District, Maryland and Virginia appear to have immunized well over 90 percent of their children.

The 90-percent goal was set for the nation in 1977 by then Health, Education and Welfare Secretary Joseph A. Califano Jr., who called it a "shocking disgrace" that millions of American children were vulnerable to seven easily preventable diseases.

The diseases, in addition to polio, are measles, mumps, rubella (German measles), diphtheria, tetanus and pertussis (whooping cough).

In April 1977, only about 60 to 65 percent of the nation's children were protected, and measles outbreaks in schools across the country that year struck 52,000 children.

Daniel C. VanderMeer, director of the HEW campaign, said there have been only 12,000 cases of measles reported this year, an all-time low. He said the country is within sight of its goal of wiping out native measles (which can cause severe mental retardation or death) by 1982.

Thousands of children are wincing or bawling in clinics and doctors' offices throughout the area this week as they receive injections to protect them against the childhood diseases. The Sabin polio vaccine which is taken orally, is the standard immunization against that virus.

While the dread of summer polio epidemics is not within the memory of today's young mothers, a recent outbreak among Amish people in Pennsylvania reminded many that the polio virus has not disappeared and still can paralyze its victims. Polio still is prevalent in some countries, and international travelers may require booster doses of the oral vaccine.

Measles, while less deadly than polio, is a major killer of children in underdeveloped countries because of its complications, particularly pneumonia. Although most children's symptoms are confined to high fever, sore throat, red eyes, cough and rash, the disease also can cause brain inflammation leading to mental retardation.

In the wake of the measles outbreaks, federal officials asked the states to survey children's health records, tighten up immunization laws and increase schools' responsibilities for student health, often through the "no shots, no school" policy.

Dr. Martin Levy, head of the communicable diseases program at the D.C. Department of Human Resources, said 95 to 97 percent of District children entering school for the first time last year were fully immunized. The comparable figure in Virginia was put at 95 percent, a 10 percent increase since 1976.

In Maryland, according to HEW figures kept by individual diseases, 97 percent of entering children were protected against measles and rubella, 91 percent against diphtheria, pertussis and tetanus, and 88 percent against polio. Those levels are believed to have increased substantially since those statistics were collected almost a year ago, HEW said.

Mumps vaccination was not included in the HEW campaign, partly because the disease is less common and considered less of a threat than measles and partly because most babies now receive mumps vaccine as part of a combination measles-mumps-rubella shot, VanderMeer said.

The disease causes painful swelling of the salivary glands in the cheeks and in men may cause sterility because of inflammation of the testicles. Brain inflammation also can occur as a complication.

Rubella, or German measles, often causes only mild symptoms and little or no rash, but if a pregnant woman contracts the disease, her child may be born with mental retardation or deafness.

Tetanus and diphtheria, while uncommon in the United States, are severe enough that even adults are advised to have combined booster shots against them every 10 years, said Dr. Alan Hinman, director of the immunization division at the U.S. Center for Disease Control in Atlanta.