Dashing the hopes of many people with chronic fatigue syndrome, an eagerly awaited study coordinated by government health agencies has not confirmed a link between the illness and a virus called XMRV or others from the same class of mouse leukemia viruses.

Two research groups had earlier reported an association between chronic fatigue syndrome and the group of viruses, known as murine leukemia viruses, or M.L.V.’s, raising hopes that a treatment or cure could be found. But later studies did not substantiate the link, and many researchers suggested that that the initial findings were the result of contamination of laboratory samples or equipment.

The new multilab study, published online Thursday in the journal Science, was designed to answer some of the questions about these unusual viruses and determine whether they posed a risk to the blood supply.

Results from another government-sponsored study of M.L.V.’s, with a much larger sample size, are expected early next year. But Thursday’s report appeared to leave little room for continued optimism.