A political catfight of headline proportions has broken out her between two of former Prime Minister Harold Wilson's most trusted intimates - former press spokesman Joe Haines and onetime political secretary Lady Marcia Falkender.

Haines, 49, was Wilson's bristling, fiercely loyal press secretary from 1969 until his boss resigned as premier last year. He managed to quarrel with almost every paper in town and abruptly ended the daily briefings for parliamentary reporters.

Lady Falkender, 44, boasts an impassioned loyalty to Wilson matched only by Haines. She went from a lower middle-class background to London University to a typist's job at Labor Party headquarters. When she was 24, Wilson chose her tfor his secretary, a post she helf for 20 years. The title understates her importance. She was political adviser, morale booster, speech editor and ruthless guardian of Wilson's inner sanctum.

The latest explosion centers on Wilson's farewell honors list, the 21 men to whom he gave peerages and knighthoods when he left office last spring. To the distrust of doctrinaire socialists like Haines, Wilson elevated a motley crew of real estate promoters, raincoat manufacturers and show business impresarios. Haines said at the time that he would not take an honor, "because I cannot dance, I can't sing and can't do impersonations."

Haines reopened the controversy in extracts in the tabloid Daily Mirror from his forthcoming book, "The Politics of Power." He claims the list was composed by Lady Falkender on her own "lavender notepaper." Haines says she "wielded power with the prime minister to a degree unequalled by any person in my experience," and that Wilson made only a few changes in Lady Falkender's list.

Lady Falkender was quick to strike back. Haines had made "wild and intemperate statements . . . probably (to) sell his book."

Sir Harold hurried over to Lady Falkender's London home and issued his own blast. "The list was drawn up by me," he said. The Haines account is "a farrago of twisted facts and alleged events that did not happen except in fevered imagination - a dedicated hatchet job."