Pamela Hansford Johnson, 69, a British novelist and essayist and the widow of the late physicist, novelist and playwright, C. P. Snow, died Thursday at a London hospital. The cause of death was not reported.

Lord Snow, to whom she married for 30 years, died last July at age 74.

Miss Johnson, who preferred to use her maiden name professionally wrote more than 20 novels, which have been published in England and the United States. Although most of the novels have love as their central theme, she was known as a strong opponent of permissiveness.

In the 1930s and 1940s, she wrote a number of stories, articles and critical reviews for English publications such as the Liverpool Post, John O'London's Weekly and The Sunday Chronicle.

Her first popular success as a novelist came in 1952 with the publication of "Catherine Carter." Other novels included "The Unspeakable Skipton," "This Bed Thy Center," set in working-class south London, "Avenue of Stone," "The Philistines," and "The Trojan Brothers," published in 1945.

Miss Johnson's other works include a trilogy, "Hungry Gulliver," a critical appraisal of Thomas Wolfe; a novel, "Girdle of Venus," which was recommended by the English Book Society; and a play, "Corinth House," which was performed in London in 1948. She also wrote book reviews for The Washington Post, most recently in April 1980.

An only child, Miss Johnson was born in London on May 29, 1912. Her father was a civil servant in the Nigerian Government Railway, her mother an actress. She began writing at the age of six and had published poetry by the age of 22. As a young woman she belonged to a circle of aspiring young writers that included the poet Dylan Thomas, who was a close friend.

A petite 5 feet 2 inches, she aspired to be an actress, but was talked out of it by her family. After attending Clapham County Secondary School, she worked as a stenographer for four years in a London bank.

Her first husband, Neil Stewart, whom she married in 1936, was a historian and journalist, and served with the Royal Artillery. Their marriage ended in divorce. They had two children, Andrew Morven, born in 1941, and Lindsay Jean, born in 1944.

She and Lord Snow had a son, Phillip Charles Hansford Snow.