More than 3,000 of the U.S. Naval Academy's 4,300 midshipmen have reported to sick call in the past week with a viral illness believed to be the Russian flu.

Physicians at the Annapolis facility saw 1,311 patients Sunday alone, and, although no samples of the virus have been isolated, Dr. James Hodges, chief medical officer at the academy, said the outbreak "fits the pattern" of the influenza that swept across the Soviet Union in a month.

Scientists at Children's Hospital National Medical Center in Washington said yesterday virus samples taken from two outpatients are "very likely typings of A/USSR/77," the proper name of the Russian virus, "but it will probably be late Friday before a scientifically accurate determination can be announced."

According to hospital spokesman Harold Kranz, Children's has experienced a "large increase in flu-like illness in the past week."

The hospital was treating as many as 150 flu patients a day in the emergency room last month before the number of casees began to fall off. Now the emergency room staff again is being overwhelmed, Kranz said, with about 150 flu patients seeking treatment each day.

Earlier outbreaks of the Russian flu were reported in this country between 1947 and 1957 in Wyoming, at the Air Force Academy and at West Point. Each outbreak was similar to the one at Annapolis, with a large number of patients contracting the disease in a very short time.

Dr. Daniel Ochsenschlager, director of the emergency room at Children's, said, "One thing that seems to be different about this is that there seems to be a fair amount of pain involved - muscle aches, leg aches, backaches, headaches, the total body-ache syndrome. It's usually in older children (who are) school age," Ochsenschlager said.

The patients at Children's and the Annapolis midshipmen also are complaining of fever, some as high as 104, abdominal pain, general aches and coughs.

"Clinically, it looks different" from the A-Texas and A-Victoria flu strains seen earlier this winter, Ochsenschlager said.

The kids (with those strains of flu were usually younger and had more (gastrointestinal) symptoms. This is more of a respiratory thing," he said.

Although its victims compalin of pain, no patient at Children's Hospital or the Academy has been hospitalized with the illness.

However, according to Dr. Alan Hinman, director of the Immunization Division of the federal Center for Disease Control in Atlanta, "The mildness of the illness seems to be as much related to the age of the patients as anything else."

Dr. James Hodges, chief medical officer at Annapolis, said yesterday, "This is my fourth winter here, and we're never had anything quite this bad. In the winter of '74 we had 300 or 400 cases in a two- to three-week period."

The current outbreak began with 54 cases last Thursday. Friday brought 154 more, followed by 143 Saturday, 1,311 Sunday, 920 Monday, 390 Tuesday and 110 yesterday.

"We have 1,200 sick as of today," Hodges said, and "about half of them will go back to classes tomorrow."

Those who contractd the flu at the Academy were confined to their rooms, except for meals, and were given aspirin and cough medicine.

The midshipmen generally have been ill three to five days, Hodges said - the same pattern experienced in the Soviet Union and in the other outbreaks in this country.

"We've kept them in their rooms for three days, and then they generally feel punk for another day or two," Hodges said.

Those most vulnerable to the Russian flu are persons between 2 and 23 years of age. persons from their mid-20s to mid-40s are likely to have immunities built up by contracting the virus when they were children or young adults. The elderly have little defense against the virus because they were not in the prime age group to contract flu when the virus last appeared.

Hodges said there have only been one or two cases of the virus among Academy personnel older than 25. None of the physicians taking care of the sick midshipmen, and none of the officers at the school, has contracted the Russian flu.

Schools and military bases are fertile grounds for such outbraks because of the large number of persons in the prime age group in close contact with one another.

Although several pharmaceutical firms are working on a vaccine against the Russian flu, no vaccine will be available for this flu season.

A panel of experts called together by Secretary of Health, Education and Welfare Joseph Califano has recommended the establishment of an ongoing federally funded program run by the states to immunize certain high-risk patients against the flu.

Among those who would receive shots under such a program would be children with chronic upper respiratory and cardiovascular diseasee, elderly persons with those conditions, others over 65 and persons in certain social service occupations, such as health care and police work.