LONDON — BRITISH voters are warning the Conservative government that its drive to reform the finances and administration of the state-funded National Health Service (NHS) may lose it the next general election.According to a Mori public opinion poll last month, two-thirds of voters believe Prime Minister John Major intends to privatize the NHS, which costs taxpayers 32 billion pounds ($55 billion) a year and employs nearly a million people. Asked whether they might let their belief sway them at the polls, half of the respondents said yes. The government insists that it has no privatization plans - only a program of reform based on market principles. But the weight of opinion believing otherwise is seen by the opposition Labour Party as one of its best hopes for ending the Conservative Party's 12-and-a-half-year domination of British politics. Mr. Major and his ministers, already well ahead with attempts to shake up a popular but ramshackle and inefficient national institution, are trying to rebut Labour's privatization charge. The prime minister gave last month's Conservative Party conference a personal pledge: The NHS would not be privatized so long as he remained in power. And William Waldegrave, the health secretary, said Oct. 30: "It is a lie to say we are trying to privatize the NHS." But Labour health spokesman Robin Cook replied that the government's program of injecting market principles into the system was "creeping privatization" and "the thin end of the wedge." Labour set up the NHS in 1948 on the basis that it would be funded wholly out of taxes and provide universal medical care free at the point of delivery. Successive postwar governments accepted that philosophy - until Margaret Thatcher, a strong believer in private medical insurance, came to office in 1979. Her advisors came up with a program of reform for the NHS. Specially trained managers were appointed to hospitals. Services such as the provision of meals to patients were put out to private tender. Three years ago, Mrs. Thatcher introduced the controversial idea of an internal "health market" with buyers and sellers, instead of the old system of hospitals spending money like government departments and doctors being paid directly out of a state fund. Mr. Waldegrave points out that spending on the NHS has quadrupled in the last 11 years, but national statistics suggest that there are still 900,000 people on hospital waiting lists. Key aspects of the changes currently planned are: * The 198 local health authorities now contract with NHS hospitals to purchase treatment needed by people in their areas. * Hospitals are becoming "sellers" of services to health authorities. So far, 57 hospitals have opted to become self-governing trusts, enabling them to set pay rates and borrow money commercially. * Doctors with more than 5,000 patients may sign contracts with health authorities, run their own budgets, and negotiate contracts with local hospitals. Major and Waldegrave have defended the changes as a bid to make the system more cost-effective. But Labour argues that the government has a "hidden agenda that, for example, NHS hospitals will be encouraged to become fully private. Voters who fear that the government has a long-range plan to abolish publicly funded medical care are probably influenced by opposition to the reforms by the British Medical Association, representing the views of doctors. In a determined attempt to turn the tide of public opinion toward acceptance of his government's good faith over the future of the NHS, Major unveiled a "patient's charter" Oct. 30 which lists the "rights" of patients and promises the creation of a mechanism to allow them to complain when such rights are not respected. David Owen, a physician and former leader of the Social Democratic Party, says "[Thatcher] used to boast about not using the NHS. John Major is very different. He believes in the NHS and he uses it. But unless the prime minister can convince the nation that the NHS is safe in his hands," Mr. Owen says, "he will not win the next election."