Doctors yesterday found a massive, inoperable spread of cancer in Sen. Hubert H. Humphrey, and his surgeon called the cancer "terminal" though he said he could not tell whether the former Vice President might live for "months" or "years."

The finding at the University of Minnesota Hospitals in Minneapolis came only 10 months after an operation at Memorial Sloan-Kettering Cancer Center in New York to remove the Minnesotan's cancerous bladder.

Doctors at that time found the cancer had spread to the lymph nodes near the bladder. National cancer statistics indicate that only 20 per cent of patients with that condition survive for five years.

Yesterday's finding obviously sharply lessens the chances of the 66-year-old Democrat, the "happy warrior" of American politics for more than 30 years.

His surgeon, Dr. John Najarian, called the discovery "a blow to us all."

At 7:45 a.m. the Minnesota surgeons began their exploratory operation to seek the cause of a bowel obstruction that had been causing the senator discomfort. They said Wednesday they hoped the obstruction would be merely mechanical, caused perhaps by scarring or some other complication of Humphrey's anti-cancer treatment.

Instead they found that the stubborn bladder cancer cells had spread to fill almost the entire pelvis, though the Memorial Sloan-Kettering surgeons last Oct. 7 removed all the cancer they saw.

The tumor extends from the right side of the body almost all the way to the left and cannot be removed, Najarian said.

There is "no way of making" any prediction "at all" about Humphrey's survival, but chemotherapy - though it will be tried - "very seldom, if ever" can eradicate such a cancer, Najarian explained.

Still, the chemicals might slow it down, he said, and there is always "hope." He said doctors at the National Cancer Institute in Bethesda feel Humphrey "would not have lived half as long as he has" if he had not been reveiving similar chemotherapy with anti-cancer drugs since last fall.

The next step, the surgeon reported, will be a new treatment plan using perhaps a "slightly different chemical cocktail" to be devised by Dr. B. J. Kennedy of the University of Minnesota and Dr. Vincent DeVita, Clinical director at the cancer institute here.

Najarian said he told Humphrey the facts "briefly" after he awoke from his three hour, 15-minute operation. He said he would speak to Humphrey again before the end of the day.

The suregon spoke at Length immediately after the operation to Humphrey's wife, Muriel, Najarian called her "the most remarkable woman I know," "objective" and "calm" and looking forward to starting more treatment.

Meanwhile, the senator is scheduled to be in the hospital for a week, then at his Waverly, Minn, home, then back in the Senate, the surgeon hoped, by "early September."

Yesterday's events came nine years after doctors first found that the then-Vice President had carcinoma in situ - cancer cells confined to a single site in his bladder. There is medical debate over whether this condition ever becomes invasive cancer, and the majority of his medical advisers decided to watch and wait.

Starting in 1972, however, he was treated with an anti-cancer drug, and in 1973 he had radiation treatment. Then last fall doctors found the plainly growing bladder cancer, and his bladder and adjacent structures were removed.

Months of chemotherapy caused most of his hair to fall out. But in recent months he had recovered and again looked hale.

Then a month or six weeks ago he began having abdominal discomfort. Only in the past week did it become clear that there was a new obstruction.

Last fall's operation forced the doctors to create an artifical opening through the abdominal wall or urination. Yesterday the surgeons had to create two more (for solid and mucuous matter) to bypass the cancerous growth.

"I don't think what happened was unsuspected," one official at the Minnesota hospital said. "I think Humphrey yesterday had a pretty good idea what the deal was."

Still the senator was reported to be his "equillient" self Wednesday, and Najarian said after yesterday's operation. "The senator seems as vigorous as ever, and I think he'll go through chemotherapy enthusiastically."