rom all parts of the country, the large cartons are coming daily to the Centers for Disease Control. Inside them are dozens of test tubes full of dark, diseased blood.

In the cluttered corridors and labs here, doctors sift the blood in scores of ways, hoping to capture the tiny virus, bacterium, fungus or whatever has infected 471 men and women from 24 states and eight foreign countries. A number of them--184--are dead. More are dying.

Whatever mysterious agent may be in these tubes, mixed with its victims' blood, three facts keep doctors here working late and uneasily:

* First, it is deadly. It kills nearly half the people it strikes. Deaths in this mysterious epidemic outnumber those in two previous emergencies put together--legionnaire's disease killed 27 in Philadelphia in 1976, and the five-year sweep of toxic-shock syndrome has killed 90.

* Secondly, the disease has no parallel. No cases in the history of medicine even suggest a disease like it, say the doctors here.

It is not an infection that is passed from victim to victim, but a loss of the body's ability to fight disease. The "immune suppression," as doctors call it, hampers the body's defenses. As a result, multiple diseases can enter and ravage the body.

* Thirdly, "The pressure is on," says James Curran, director of the CDC task force, to find the killer. "Legionnaire's disease in 1976 was one event. In toxic shock the cases started going away when some tampons came off the market. But this isn't going to stop. It's increasing. We now have 250 percent more cases in the last two months than in the first two months."

The disease has mainly attacked four groups, but Curran says, "There may be additional groups that get it, and in the other groups people are going to keep on dying. . . . Somebody's got to find this thing."

CDC officials say the American population at large is not at risk now and may never be at risk. For most of the year of the epidemic the groups affected have been male homosexuals and drug users who use needles to inject their drug.

In the past two weeks, the CDC has issued bulletins naming two other groups. First, 34 Haitian immigrants--reportedly healthy, heterosexual men and women with no history of drug abuse--fell victim. Half of them have died.

Then three people with the blood disorder hemophilia, which prevents clotting, came down with the disease. They, too, were healthy and heterosexual. Two have died.

In addition, between 10 and 20 men and woman reported as victims of the disease apparently belong to none of the four groups.

Who may be the next victims?

"People like us," said Curran. "Doctors. Hospital staff. Oral surgeons. People who handle blood."

The mystery started more than a year ago when doctors at CDC noticed an odd item in their reports. A rare pneumonia, found only in patients whose immune defenses are down because of drugs given for other diseases, had turned up in four Los Angeles men. They were young and otherwise healthy. All were homosexual.

Not long afterward, cases of Kaposi's sarcoma--an extremely rare cancer in this country--turned up by the dozen in New York City. Kaposi's previously was found only in old men and those whose immune defenses were down because of some therapeutic drug.

These victims, too, were young, generally healthy, and homosexual.

Doctors soon saw a variety of diseases striking young homosexual men in a similar pattern, and found that in all cases, the immune systems of the men had been debilitated, allowing the cancer and other infections free rein.

The first symptoms of the disease apparently are enlarged lymph nodes, a feeling of malaise, sometimes low-grade fever and weight loss. The symptoms can last months without becoming serious.

"It is obvious that most of the people who get it simply don't know they have it until they get one of these other opportunistic infections," said Bruce Evatt of the CDC task force. "These people are like walking time bombs."

The "opportunistic infections" are most commonly the Kaposi's cancer, a virulent pneumonia called pneumocystis pneumonia, toxoplasmosis which can affect the central nervous system, candidiasis yeast infection, or an odd variant of tuberculosis called atypical mycobacterial infection.

Though each of these ailments can be treated, there is no treatment for the underlying failure of the immune system. So the diseases recur again and again, sometimes together. In about half the cases the patient finally dies.

Of the 471 who have contracted the disease, none has recovered from the underlying failure of the immune system, but some are now free of deadly infections.

Dr. Harold Jaffe of the CDC was one of those who early went to New York to study the cases, searching for anything the victims had in common that might give a clue about the mysterious disease.

Two discoveries stuck out: the victims were not only homosexual but hypersexual (one reporting, for example, sex with more than 1,100 partners); secondly, all had used amyl nitrite or butyl nitrite, or "poppers," to enhance sexual experiences. It seemed for some time that the nitrite drugs might have an effect on the immune system and the disease could be spread by sexual contact.

But soon, other victims were found who were not homosexuals and did not use poppers. They were the drug addicts.

Many victims appeared also to have or have had infections of cytomegalovirus (CMV), a virus that affects the immune system. But tests in different parts of the country found no one strain of the virus in all victims.

"Six months ago we were all looking at nitrites for the cause. Now we're all looking to the virology lab for the answer," says Dr. Kenneth Hermann.

He swings open the white metal door of what looks like a walk-in meat locker. But inside it is hot, and filled with racks of test tubes holding specially prepared cultures and samples of blood, urine, semen, stool and tissue from disease victims.

If the epidemic is caused by a deadly virus, it should multiply here. In larger numbers the viruses can be seen under an electron microscope, or their presence detected by radioactive labeling.

In the hallways and cluttered labs here, dozens of white-coated technicians move about carrying racks, pushing buttons on equipment, writing in logs--all in the hope that the culprit is a virus.

But the mysterious agent may not be a virus at all. Or, if it is a virus, it may not be one that grows in culture. Or it may be present in the samples in such small numbers that it will be missed in tests. The list of doubts is endless.

The best running theory is that the killer is an agent, probably a virus, that is transmitted through the blood or other body fluids. For homosexuals it is orally or through semen. For drug addicts it is from passing blood-encrusted needles. For hemophiliacs it may be the blood concentrate they must take daily, obtained from blood banks.

The problem is a frustrating one for the scientific detectives.

With Legionella--legionnaire's disease--doctors were sure at once that they were dealing with an infectious agent that caused disease very quickly. There was a common source of infection--the hotel the initial victims stayed in--and many medical specimens came in all at once to test.

This killer, said Hermann, "is more nebulous, slowly emerging over months and years. We don't have any diseases that even resemble it, human or animal diseases." Cell tests for one patient take months.

In a nearby building, Dr. John Bennett, deputy director for infectious diseases, worries out loud: "This thing is just ripe for hysteria. I mean, possible death from an unknown agent. . . . It should be made clear that it isn't an immediate threat to most people now."

Curran said that other agencies were swinging into action to combat the epidemic. The National Institutes of Health, he said, will form its own task force.

At the Department of Health and Human Services, Undersecretary for Health Dr. Edward Brandt has formed a public health service committee to report within 30 days on what to do about blood collection and distribution now that it seems possible that some of the collected blood may be diseased.