Roman Catholic Church leaders and British officials here are pleading with Pope John Paul II not to cancel his scheduled historic visit to Britain at the end of this month because of the undeclared war over the Falkland Islands.

Prime Minister Margaret Thatcher said tonight in a radio interview here that she hoped "very, very much" that the pope would still come to Britain. "So many people are looking forward to it," she said. "So many people have made endless effort to see him and to organize things for him."

Church leaders fear that the pope will decide this week to cancel the six-day visit scheduled for May 28 through June 2 unless there is an unexpected breakthrough in peace talks at the United Nations. As sporadic combat continued in the South Atlantic and a British invasion of the Falklands appeared imminent, the pope warned yesterday that "the context of the visit can only be one of peace and serenity."

In a last-minute attempt to change his mind, the archbishops of Liverpool and Glasgow went to Rome today to argue that the pope could still come to Britain if he also announced that he would visit Argentina as soon as possible, according to Cardinal Basil Hume, Catholic primate for England and Wales.

Hume said the archbishops also hoped to impress the pope with "the degree of disappointment" among all Britons, including the 10 percent Catholic minority, about the prospect of cancellation of the first papal visit to Britain since Henry VIII broke with Rome in the 16th century. The papal visit had been envisioned by both Catholic and Anglican Church leaders as an important symbol of their growing movement toward Christian unity here.

A Gallup Poll published in yesterday's editions of the Sunday Telegraph newspaper showed that two of three Britons want the pope's visit here to go ahead as scheduled. Those favoring the visit included 77 percent of the Catholics polled and 62 percent of Church of England members.

Pointing out that Catholics here blame Argentina for causing the hostilities that may be the cause of a cancellation of the papal visit, Hume said, "They feel if the pope doesn't come that he is punishing English Catholics."

Catholic Church sources here said they believe the pope is being advised to stay away from Britain by aides who are in close contact with the church in South America, which has the world's largest Catholic population