WASHINGTON (AP) _ British agents planted propaganda in American newspapers, harassed political enemies in Congress and labor unions and waged economic warfare in this country in the years before Pearl Harbor, according to a secret history quoted by the Washington Post in Sunday editions.

Agents headed by Sir William Stephenson, celebrated in the 1976 book, ''A Man Called Intrepid,'' waged their campaign out of an office in Rockefeller Center in New York known as British Security Coordination, the history said.

The Post said 10 leatherbound copies of the 423-page document prepared in 1945 were said to have been distributed but that none have surfaced until now. The newspaper said it was allowed to take extensive notes on a copy of the history but did not name its source.

Several American newspaper publishers as well as columnists Walter Lippmann, Walter Winchell and Drew Pearson were described as helpful to the British effort to discredit isolationism and harass Nazi sympathizers.

The history portrays America on the eve of World War II as easy to manipulate. ''These people, though fully conscious of their wealth and power in the aggregate, are still unsure of themselves individually, still basically on the defensive ...'' the Post quotes the history as saying.

It quotes the history as detailing a media campaign against Gerhard Alois Westrick, allegedly a German agent in the United States with close ties to Torkild Rieber, the president of Texaco.

A ''first class news story'' was ''written by BSC and placed through an intermediary in the New York Herald Tribune ...'' under headlines such as ''Hitler Agent Ensconced in Westchester,'' the history said.

''Westrick was deluged with threatening telephone calls,'' it said. ''A hostile crowd gathered outside his house.'' His American contacts deserted him, according to the document.

The history said a British front group called Fight for Freedom passed out 25,000 handbills at a September 1941 speech in Boston by isolationist Sen. Gerald P. Nye, attacking him as ''an appeaser and a Nazi lover.'' It said British agents tried unsuccessfully to sow confusion at an America First rally at Madison Square Garden a month later by distributing duplicate tickets.

The history said the British started a rumor mill. ''Objectives ranged all the way from publicizing misleading information about allied strategy to undermining the prestige of an individual Nazi by encouraging salacious gossip about his private life.''