BARELY HAD THE WORLD begun to absorb the sad news of his inoperable cancerous tumor when the incredible Hubert Humphrey was letting it be known that he is gearing up for a prompt return to the Senate "to vigorously pursue those matters which are of vital interest both to Minnesota and to the nation." And anyone who knows Hubert Humphrey - well, by golly, you'd better believe he's going to do his ever-lovin' darndest to be back at the old stand on time, with that clearly limitless verve and who-knows-how-many things to talk about.

We can't help recalling his last bout in the hospital in October, when the irrepressible senator literally took over the eighth floor of the Memorial Sloan-Kettering Cancer Center in New York. There he was, doing his rounds, prodding patients out of their wheelchairs, shaking hands with everyone in sight and generally infusing gaiety and hope into a normally somber ward. The place, it was reported, was transformed.

Then, as now, Hubert Humphrey just wasn't about to let gloom set in. "I've had enough tests to go through 44 universities," he quipped on his return to Washington, proceeding to talk fondly of all the patients he'd visited regularly throughout his stay: "They say I helped those people, but oh, how they helped me." Now again we find Hubert Humphrey hospitalized and characteristically diverting attendion from his own difficulties. After asking the hard questions of his surgeons and being "discouraged momentarily" by the answers, he's off bounding down the halls against doctors' wishes; he's meeting with his staff to talk about the Panama Canal treaty and other Senate business. "He's been walking so fast we've almost had to give him a speeding ticket," said one of the surgeons yesterday.

All this, of course, is why Hubert Humphrey has barnstormed his way into the hearts of people everywhere. Some people have seen in the senator's energy and exuberance and verbosity a self-indulgence of sorts, a lack of self-discipline and self-control. They make a very superficial reading of the man. For the key to Sen. Humphrey's achievement and grace is and always has been an extraordinary ability to control - in fact transcend - those elements ofself that distract and even destroy so many others: vindictiveness, pettiness, self-pity, spite. It has been this special capacity that has given him size as a human being - and the energy to keep at it. So in planning his return to the obvious, unabashed joy of politics and people, ubert Humphrey should know that Americans everywhere are - as he would put it - "pleased as punch" at the prospect.