All blood that comes from paid, often Skid Row donors will be labeled "paid donor" soon to discourage its use and try to prevent thousands of cases of blood-borne liver disease in American hospitals.

After years of delay - and opposition from much of organized medicine - the Food and Drug Administration is about to order that the 10 million units of blood used in transfusions and other treatments each year be plainly marked "volunteer" or "paid donor."

The main aim is to prevent the serious liver disease, hepatitis, Dr. Donald Kennedy, FDA commissioner, said in an interview.

By various estimates,enough unsuspected hepatitis virus is present in transfusion blood to cause between 17,000 and 30,000 hepatitis cases a year.

Paid-donor blood causes 5 to 10 times as much hepatitis as volunteer blood, simply because so much of it comes from undernourished, habitually diseased persons, estimated Dr. Tibor Greenwald, medical director of the American Red Cross and one of the nation's leading authorities on medical blood use.

The use of paid-donor blood has dropped shrply in recent years as a result of a federally insipired effort to move the nation toward an all-volunteer blood system.

Five years ago 16 per cent of all blood used was paid blood. Today the figure is estimated at someplace between 5 per cent and 10 per cent.

"Even if it's only 5 per cent, that's still 500,000 bloods," Greenwald said. "Those 500,000 transfusions will cause more hepatitis than the transfusion of 5 million units of Red Cross volunteer blood."

"Blood collected by commercial blood banks from paid donors is clearly high-risk blood, and we want it labeled," said Dr. Lewellyn Barker, FDA blood and blood products director.

Blood - the chemical that carries oxygen, fights disease and flushes waste gas from our bodies - is one of modern medicine's vital serums.

Millions of transfusions of whole blood are used after accidents and in surgical operations. Much blood is also separated into red cells, platelets and other components, each to be given for different conditions.

"One pint of blood may go to four or five patients today," Greenwald said.

Nearly four years ago then-Health, Education and Welfare Secretary Caspar Weingberger called on the medical community to develop a system to provide enough safe blood for everyone without buying any on Skid Rows.

Most of the groups handling blood soon formed an American Blood Commission to try to work toward an all volunteer system.

Today 58 Red Cross blood centers collect enough from volunteers to provide hall the nation's needs. Nearly 50 non-profit community blood banks collect another 15 per cent, and hospital blood banks about 25 per cent.

There are also between 25 and 40 commercials banks - the number is unsure, since they do not have to be licensed in many cases - concentrated in major cities like New York, Chicago, Philadelphia, Los Angeles, Dallas, Houston and Baltimore.

They pay donors from $25 to $50 a pint of blood and resell it to hospitals or various processors, Greenwald said.

Strenous efforts are made at many blood centers to screen both paid and volunteer donors and their blood for hepatitis virus. But a test exists for only one of two major types of hepatitis, the test is not always sucessful, and it has been learned recently that there are one or more unidentified strains of virus that also carry the disease.

In November, 1975, the FDA proposed that paid blood not only be labeled but also carry a sticker warning of possible disease. Protests from many doctors and hospitals made the FDA retreat.

Las Feb. 25, in a formal notice in the Federal Register, it proposed only that the volunteer or paid source be identified.

"We think that's adequate," Barker said. "Doctors know enough now about the dangers of paid blood to be wary of using it if it's identified."

The new rule has still been opposed by the American Medical Association and the American Association of Blood Banks, representing hospital banks.They argue that both volunteer and paid blood can transmit the disease, and that many hospital banks screen donors and blood to prevent it.

Greenwald maintained that "I know for cetrain of only one hospital blood bank," that of the Mayo Clinic, that uses paid donors with a high degree of safety. It buys blood only from its proved hepatitis-free donor group.

The Feb. 25 Federal Register notice allowed 60 days for comment before making the new labeling rule effective June 27. The notice period expired last week.

"We'll move quickly now," kennedy said. "All the evidence is on one side."