Muriel Humphrey Brown, the archetypal political wife who stood by Hubert Humphrey during his more than 40 years of government service and then filled his Senate seat after his death in 1978, died Sept. 20 in Minneapolis. She was 86.

Mrs. Brown was admitted to Abbott Northwestern Memorial Hospital earlier that day and died of natural causes, officials said. She had been out of the political spotlight for years but made a rare public appearance last week to see her eldest son, Hubert H. "Skip" Humphrey III, win Minnesota's Democratic state gubernatorial primary.

"Hubert would have been proud," Mrs. Brown told a cheering crowd.

Although she was known for her soft-spoken, gentle ways, she changed the rules of presidential campaigning during her husband's bid to become the Democratic Party's nominee in 1960. Traditionally, a candidate's wife was little more than a prop, but she was one of the first to strike out -- and speak out -- by herself on the campaign trail.

Former vice president Walter Mondale, a Hubert Humphrey protege who knew Mrs. Brown for 50 years, said the Humphreys were a fantastic team both in public and at home.

"Together they helped change this country to a better, fairer, more decent society," Mondale told the Associated Press. "Half of what we credit Hubert for we should credit Muriel {for}, because they were a team from beginning to end."

Mrs. Brown was born Muriel Fay Buck in Huron, S.D., on Feb. 20, 1912. She married Hubert Humphrey in 1936. She rang doorbells in a door-to-door campaign for her husband when he successfully ran for mayor of Minneapolis in 1945, and she was at his side when he was became a U.S. senator three years later. In 1964, after twice being reelected to the Senate, he stepped down to become Lyndon B. Johnson's vice president.

Campaigning didn't come easily for Mrs. Brown. According to one account, she was asked to speak before a group of prominent San Francisco lawyers during the 1960 campaign and was so nervous that her knees shook and her voice quavered. But her Midwestern charm and unassuming directness won over the crowd, and the lawyers gave her a standing ovation.

She sharpened her political skills during her husband's failed 1968 and 1972 presidential campaigns, as well as his successful campaigns for the Senate in 1970 and 1976. She once baked cookies for reporters. While other wives of presidential candidates spoke vaguely about how effective their husbands could be if elected, she talked about how much she'd like the job of first lady.

"I'd love to be first lady," she once told a reporter. "It's like giving me a magic wand with which to help programs I believe in."

After the birth of a mentally disabled granddaughter, she became a crusader for the disabled, serving on a Johnson-era committee on mental retardation and promoting other projects related to mental health.

When Hubert Humphrey died after a long battle with cancer in 1978, she was appointed to fill his Senate seat. She was the only female senator at the time and was only the 12th woman to serve in the Senate.

Mrs. Brown took her place in the Senate on Feb. 6 of that year, vowing to continue working on the legislative program left behind by her legendary husband.

"I hope I can do as well," she said with characteristic modesty. "I hope I can fill Hubert's shoes."

Like her husband, she pushed labor issues and social programs, but she also went on to lobby for abortion rights and the Equal Rights Amendment. She decided to step down when her term expired in November 1978.

She married a high school classmate, Republican businessman Max Brown, in 1981. She and her second husband split their time between homes in Minneapolis and Nebraska, where she devoted herself to being a grandmother, doing needlepoint and tending to her flowers.

With her health and stamina failing, Mrs. Brown all but dropped out of politics in the 1980s, campaigning only for her son. "I don't have the energy for it anymore," she said. "It's such an exhausting process. Yet I can't help thinking about the course of the country. I still care a great deal. After you've spent that many years at something, it's not all that easy to drop it."

In addition to her husband and her son Skip, Mrs. Brown is survived by two other sons, Bob and Douglas Humphrey, and a daughter, Nancy Solomonson. CAPTION: Muriel Humphrey Brown filled her husband's Senate seat after his death in 1978. ec