LONDON, FEB. 3 -- Thousands of British nurses staged a 24-hour strike today to protest low wages and what they charge is the overall underfunding of Britain's National Health Service by Prime Minister Margaret Thatcher's government.

The strike, which was centered at 42 London hospitals but affected medical institutions throughout the country, was called by unions representing about half of the nation's government-employed nursing corps.

In a separate action, the British Medical Association called today for an emergency cash injection of up to $2.6 billion to cover current financing shortfalls in government-owned hospitals.

Thatcher charged that the strike would "gravely damage" patients, and her government condemned the protests as "deplorable." Most hospitals, however, were reported operating normally with temporary and nonstriking nurses, although nonemergency surgery was canceled for the day in many places.

The nurses' strike marked a high point in what has now been several months of steady complaint about the government's management of the health service. Although Thatcher's massive majority in Parliament gives her the strength to ride out any extended protest, the health service debate has forced her government into a more defensive posture than any issue over the past nine years.

Health care is always a highly emotive subject in this country, where 99 percent of all citizens are registered with the state-owned and -operated service designed to give them free, cradle-to-grave care. Repeated public opinion surveys have shown that a large majority agree with health care professionals that the health service's quality has been slipping badly.

The current crescendo of criticism started last fall, when many hospitals found themselves out of money and forced to close down entire wards. At the same time, waiting lists around the country for elective surgery had surpassed 600,000 people, with many waiting for a year or more.

The government in recent years has imposed strict spending limits on hospitals, ordering them to increase efficiency and find new ways of raising money to fund expansions and service improvements.

Political opponents have charged that Thatcher set out to create a crisis in the service to pave the way for easier public acceptance of increased private health care. Last week, Thatcher said that the government is conducting a comprehensive review of how the health service is funded.

Pending the results of that review, the government has refused to pump more money into the system, either to overcome the current emergency shortfalls or to increase nurses' pay substantially. That position has outraged opponents, since the government is reported to have a budget surplus of nearly $20 billion this year.

According to a poll in this morning's Daily Telegraph, 92 percent of the public, including 9 out of 10 members of Thatcher's Conservative Party, sympathize with the nurses and believe they should have a substantial raise. Basic nurses' pay throughout the system is about $12,000 a year, about the same as that of bus conductors and far less than police or firemen.

Much of the hospital waiting list problem is caused by nursing shortages, as large numbers of nurses have left the profession or found better-paid nursing jobs in Australia, New Zealand and the United States -- all of which have energetically recruited here.

Not all nurses believe that striking is the best way to bring pressure on the government. The Royal College of Nurses, which represents about half of Britain's 500,000 nurses, is pledged by its own bylaws not to strike. The union's officials said today that the actual number of striking nurses, represented by two other public employee unions, was smaller than news reports had indicated, and said that picket lines had been augmented by students and hospital auxiliary workers.

But picketing nurses, many of whom were in uniform, vehemently disagreed, and said that their numbers were in the thousands. They said that the strike had been carefully organized to make sure that only those who could be spared from necessary patient care would come out on the picket lines.