Sen. Hubert H. Humphrey, weakened by a spreading cancerous tumor, was listed in critical condition yesterday at his home in Waverly, Minn.

Humphrey's administrative assistant, David G. Gartner, said the senator was "resting comfortably" and hospitalization was not anticipated.

Gartner's statement, issued in late afternoon, said Humphrey had "noticeably weakened and is listed by his doctor as being in critical condition."

The former Vice President, 66, drawn and pale from his long battle with cancer, has been home since Dec. 22, when he flew to Minnesota aboard Air Force II with Vice President Mondale.

Earlier this week, an aide said the senator was "hopefula" that he could return to Washington in time for the reconvening of Congress next Thursday.

But yesterday, according to sources in Minnesota, members of Humphrey's immediate family were called to his bedside in Waverly as his condition worsened.

On his return to Minnesota last month.Humphrey said he had no plans to give up his Senate seat unless he became "totally incapacitated" - an eventuality that his tone suggested would be impossible.

Humphrey entered the University of Minnesota hospitals on Aug. 16, to undergo surgery for an intestinal blockage. Two days later, operating physicians found cancer cells embedded in his pelvis and called the condition inoperable.

Doctors said that spread of the disease could be checked for a time with chemotherapy - a painful treatment process that Humphrey once called "bottled death."

The university hospitals' chief surgeon, Dr. John Najarian, said the pelvis tumor undoubtedly was a regrowth of a bladder cancer that had led to major surgery less than a year before.

On Sept. 2, looking thinner and grayer, the former Vice President left the hospital and went home to Waverly for a 41st wedding anniversary celebration with his wife, Muriel, the next day.

In the spirit that made him an inspiration to friends and colleagues and fellow cancer victims, he told an audience of cheering labor delegates two weeks later, "I'm not about ready to have somebody cover me up."

The Humphreys returned to Washington on Oct. 23 as guests of President Carter, who diverted Air Force I from a cross-country flight to stop for them in Minneapolis.

A few days later, when the senior senator from Minnesota - he has been a senator off and on since 1949 - went back to Capitol Hill he was greeted by an effusive show of affection from Democrats and Republicans.

As he bounded onto the Senate floor, Humphrey fell into an embrace with Sen. Russell B. Long (D-La.), often a foe on controversial legislation, amid long and warm applause.

A week later, in an equally emotional session in the House, Humphrey received more accolades as the non pareil liberal leader, champion of the underdog, patriot who held no grudges.

"He kills his enemies with love," said Rep. Morris Udall (D-Ariz).

A member of the esteem in which Humphrey is held outside the Congress was the contributions and pledges of more than $1 million generated by a "national tribute" dinner her Dec. 2.

The money, part of almost $6 million received so far, will help finance the Hubert H. Humphrey Institute of Public Affairs at the University of Minnesota, from which he graduated Phi Beta Kappa in 1939.

Last month, after Mrs. Humphyrey was released from a brief hospital stay from treatment of heart disease, they sent home to Minnesota on Mondale's plane.

As he stepped down from the plane, Humphrey appeared to walk with difficulty. His face was gaunt, he seemed thinner but the familiar smile of the "Happy Warrior" was on his lips.

No, he said, he wouldn't be resigning. And then a quip: if anyone was planning Christmas gifts, he wanted it know that his shirt size had shrunk a bit.