A 6-year-old Maryland girl hospitalized here last month had only a "flu-like illness," not swine flu as briefly suspected, U.S. disease experts reported yesterday.

Georgetown University doctors had sent a suspected swine flu virus - grown in material from the girl's throat - to the Maryland Health Department and the federal Center for Disease Control in Atlanta for study.

CDC scientists gave their verdict yesterday. They said the virus was almost certainly a laboratory strain of swine flu used as a "reference" or "control" strain - one to grow alongside any new-found virus for comparison.

The lab strain evidently contaminated the new sample, Dr. Robert Craven of CDC reported.

"It's 99 per cent certain this is the case," added Dr. Stephen Thacker, CDC epidemic intelligence officer at the D. C. health department. "But what Georgetown Hospital did was perfectly reasonable. They had suspicious culture, so they sent it to CDC for confirmation."

The possibility of swine flu in the child was announced Friday, not by Georgetown University but by the Maryland Health Department. Yesterday the Prince George's County Health Department said that "intensive field investigation" in the girl's school and neighborhood in southern Prince George's County had found no unusual illness or influenza, though the girl's father and mother had been briefly ill, too.

The girl was hospitalized Jan. 31 and released Feb. 2. Health officers would not disclose her name.

If the girl had turned out to have swine flu, she would have been one of a mere handful of such patients in the United States since that disease affected several Ft. Dix. N.J., recruits and killed one in January, 1976.

That incident, and the fear that this new flu strain might spread, set off a nationwide vaccination cmapaign that was ended in December because one vaccination in 119,000 was causing Guillain-Barre disease, a form of paralysis. The moratorium was partly lifted last week so doctors and health departments can give combined A'Victoria-swine flu vaccine to older and chronically ill persons to prevent spread of A'Victoria flu.

Georgetown doctors took a throat swab from the girl ad tried to cultivate a virus because her doctors requested it to diagnose her condition.

Not every respiratory or flu-like illness in every hospital is studied this way. Instead CDC disease detectives rely on a nationwide network of reporting doctors, hospitals, schools, work places and health officers to report any apparent flu and take cultures from individuals so any epidemic can be quickly spotted.

There had been no more spread of A/Vcitoria flue since a Miami nursing home outbreak caused the federal government to order the partial end to the vaccination ban.

There have been outbreaks of usually milder B/Hong Kong flu in many schools throughout the country, and DCD officials have asked state authorities to start reporting cases of an occasionally serious complication, a brain and liver disease called Reye's Syndrome.