The British law in fact applies only to transplants performed in the nation's private hospitals and not to those overseen by the government-supported National Health Service, which provides free medical care for British citizens. The service, which has not used paid donors, gets first pick of all kidneys available for transplant in the nation. At present, about 1,600 transplants are performed each year, with a waiting list of about 3,600 patients.
But as in the United States, many patients from countries without high-quality kidney care come to Britain each year to undergo transplants in private hospitals. These hospitals, including London''s Humana Hospital, Wellington, where Mr. Benton's transplant took place, rely on cadaver kidneys or live donor transplants from relatives of patients. 'Paying to Survive'
In the past, doctors simply questioned foreign donors to make certain they were related to recipients, but most admit the system was hardly foolproof. Often doctors could not communicate with patients who did not speak English. A doctor involved in the Benton case said he attempted to find out if the donor had been paid by waving a $:5 note at him.
''A number of us were duped by patients with forged medical referrals and documents saying they were relatives,'' said Maurice Slapak, director of the transplant unit at St. Mary's Hospital in Portsmouth.
Despite the speed and ease with which the British transplant law was passed, it remains controversial. In a letter to The Times of London, Royden Harrison, professor emeritus of social history at Warwick University, wrote: ''What possible objection can there be if one person, of their own free will and without duress, should sell their kidney to someone else? The seller is able to indulge in a few of the good things in life. The buyer may well be paying to survive.''
Sir Michael McNair Wilson, a conservative member of Parliament who is on a waiting list for a new kidney, has argued that selling a kidney is like women in the 19th-century selling their hair.
''As someone waiting to receive a transplant, I would only like to feel that the organ I am given is a gift from someone,'' he said. ''But while there is a shortage of kidneys, I do not see why it is wrong for you to do what you will with your body.'' Incentives to Donate
Dr. Swerdlow of the Annenberg Program suggested that organ donations could be encouraged if the survivors of people whose organs are donated for transplant received Federal money to cover funeral expenses. Or, he said, a tax deduction could be applied to a donor's final year of taxes or estate taxes. Some have even suggested that people could sell future rights to their tissues and organs in return for lower insurance premiums.
''If it takes $25,000 to $30,000 annually to keep someone alive on an artificial kidney machine,'' John M. Newman wrote in the Annenberg Program report, ''government payment of, for example, $5,000 for transplantable cadaver kidneys (even with the cost of transportation), would still make sucessful kidney transplantation cost effective.'' Dr. Newman, a kidney transplant recipient, is a director of the American Association of Kidney Patients.
''This is not to suggest that a monetary value can be placed on human life or on life-saving organs,'' he added. ''This does suggest, however, that a monetary 'thank you' from the Federal Government could stimulate increases in organ and tissue availability for transplantation and research.'' Fear of Scaring Off Donors
In Britain, there is concern that the new law could scare off suitable donors and add to the shortage of kidneys by somehow creating the impression that all donations are improper.
A report today by the National Kidney Research Fund said there had been a dramatic fall in the number of kidney donations earlier this year following the kidney-for-sale controversy. ''There have effectively been at least 100 fewer transplant operations this year, and that means 100 people may have died because of the unfavorable publicity,'' the organization said in a statement.
Critics of the new law also point out that the Benton case and others like it had been investigated under previous laws.
One investigation led in May to the conviction and imprisonment in Turkey of 55-year-old Tunc Kunter, the kidney broker who recruited the Turkish donor for Mr. Benton's operation. Lawyers for Mr. Kunter, who was jailed for two years, claimed that under Turkish law doctors are responsible for ensuring that the organs used were not part of a cash transaction.
During the trial in Ankara, Ata Nur Kunter, the defendant's brother, was described as a London middleman in the kidney trade. He also maintained that he was a ''business associate'' of one of the London doctors involved in the transplants at Humana Wellington.
Two London doctors are being investigated by Britain's General Medical Council for their roles in the Benton operation. The council would not comment on the case. Humana Wellington was forced by the Department of Health to close its transplant wing earlier this year, but it was allowed to reopen in May after tightening its procedures for transplants. Automatic Donations Suggested
Some opponents of the law simply think the it is addressing the wrong health issue. Elizabeth Ward, founder of the British Kidney Patients Association, supports legislation that would make make organ donation automatic upon death. Those who chose not to donate would have to make a formal request.
''It would solve the problem of kidney shortages,'' Mrs. Ward said.
But Belgium began such a program in 1987, and it has had little effect, said Jozef Devoss, an official at the Belgian Embassy in London.
''Doctors are quite reluctant to use the law,'' he said. ''Doctors still ask next of kin for permission to remove organs. It's a moral issue.''
Nevertheless, many in the medical profession here think the law was needed.
''If we take the very extreme view, people in desperate circumstances might be prepared to martyr themselves, selling their hearts to save their families,'' said Ross Taylor, director of transplant surgery at the Royal Victoria Infirmary in Newcastle Upon Tyne and president of the British Transplantation Society. Mr. Taylor also criticized those tempted to sell their organs for frivolous reasons. ''I have met people prepared to sell their kidneys to buy Porsches or to take a girlfriend on a holiday.''