Alabama Gov. George C. Wallace's surprise pullout from the 1978 Senate race has ended - at least temporarily - one of the most controversial and colorful American political sagas of the 20th century and has set the stage for a new kind of politics in his state.

At a news conference yesterday in Montgomery. Wallace said little to clarify the reasons that lay behind his sudden announcement. Tuesday night that he would withdraw from the Democratic primary contest to succeed retiring Sen. John J. Sparkman (D-Ala.)

But Alabama political sources asserted that it was a combination of adverse polls and the physical demands of a strenuous race that drove Wallace to the sidelines.

"I just decided I didn't want to run," said Wallace, 58, who has been confined to a wheel-chair since an assassination attempt during his third presidential campaign in 1972 left him permanently crippled.

Completing his second consecutive term as governor, Wallace is ineligible to run for reelection, and Alabama's other Senate seat is held by his close friend. James B. Allen (D-Ala.).

But Wallace - ever one to preserve a shred of suspence - told reporters. "I did not say I was necessarily retiring from politics, and I did not say that I am not."

His withdrawal left. Howard Heflin, the former chief justice of the Alabama Supreme Court, as the front-runner in a Democratic primary field that also includes two young state senators, Donald W. Stewart and John Baker.

But there were indications that at least one more serious challenger may enter the Sept. 5 primary. Rep. Walter Flowers (D-Ala.) of Tuscaloosa, a 10-year House veteran, said through an aide he was "considering very seriously" joining the field, but would not decide until next week.

At the Montgomery news conference, Wallace warded off repeated attempts by reporters for details of his decision. "I have reasons known only to myself." he said "Let's not make a federal case of it."

He said he made the decision after an overnight visit to Gulf Shores, a resort community not far from Mobile. "I had time to think, away from the telephone," he said. "I was by myself for a day and a half."

The dramatic announcement was tacked onto the end of an otherwise ordinary speech to a gathering of state officials in Mobile. Yesterday, Wallace suggested that he had been ambivalent about making the statement Tuesday night right up until he said it. "I almost did not make it," he said.

Wallace's political saga was one of the most extraordinary of modern times. He controlled the Alabama state government for all but two of the last 16 years, and in that period ran four times for the presidency, developing a national constituency that numbered in the millions.

Yet in the end he was a lonely man, fined to a wheelchair and openly wor-fined to a wheelchair anl openly worried about funds and personal aides he needed to survive as an invalid.

That was a far cry from the cocky little "fighting judge" who won the governorship on his second try in 1962 and used his inaugural to sound his cry to defiance to Washington: "Segregation now! Segregation tomorrow Segregation forever!"

There was widespread speculation that declining polls, fund-raising problems and the physical challenge involved in a strenuous campaign may have contributed to Wallace's decision.

One campaign consultant involved in a rival's campaign said bluntly: "Wallace was either going to get out or he was going to get beat."

But Wallace discounted these problems, and a close friend said the main reason was pressure from his four children - two married daughters, a son in law school and a daughter who is being graduated from high school next month.

"The family has been denied a father for a long time," said Charles Snider, who managed Wallace's last two presidential campaigns.

Polls that surfaced yesterday in Montgomery, Atlanta and Washington showed Wallace in a virtual dead heat with Heflin, even though the governor enjoyed a decided advantage in name familiarity - not a healthy situation, in the eyes of campaign managers.

Wallace told reporters, "My health is in good shape," but friends have been saying for months that they wondered whether he was up to the demands of a tough battle.

Even though he was wearing a hearing aid at yesterday's press conference, Wallace often did not hear questions shouted at him from a distance of only a few feet. His press secretary, standing behind the governor, repeated questions for him.

But despite this disability, Wallace flashed some of his old humor in his session with the reporters.

After repeated questions about how he reached his decision, Wallace quipped: "Maybe a little fairy talked to me while I was asleep."

He told the reporters that his greatest regret in dropping out of the campaign is that "I won't have this crowd to kick around any more."

Wallace said he would not endorse any of the other candidates for Sparkman's seat, and said he had no plans after January, when his term ends. Funds are reportedly available to finance a teaching chair for him at the University of Alabama, but aides discounted the chances of his taking such a post.

Those same aides, however, conceded that they were caught by surprise by Wallace's Tuesday night announcement.

Asked what would be the effect on Alabama politics of his apparent retirement, Wallace answered drolly: "It will cause a great upheaval, almost volcanic in nature."

In 1964, Wallace made a surprisingly strong showing in three presidential primaries against stand-ins for President Johnson, vowing to "shake the eye teeth" of the "pointy-headed bureaumats" he said were running the country.

Two years later, barred by a since-repealed provisions of the state consituation from seeking reelection, he ran his first wife, Lurlee, for the job and saw her win handily. When she died of cancer in midterm, she was succeeded by Lt. Gov. Albert Brewer (D).

Wallace ran for president again in 1968, this time as an independent, carrying five states and winning almost enough electoral votes to deny a majority to either of the major party contenders.

In 1971 he ran again for governor, defeating Brewer in a bitter runoff struggle. Two years later, he again threw a fright into the Democrats by launching a series of presidential primary vimories with a strong showing in Florim.

But while campaigning at the Laurel, Md., shopping center that spring of 1972, Wallace was the target of an attack by Arthur Bremer that left him permanently paralyzed below the waist and with serious internal wounds.

He continued his political career, winning reelection as governor easily in 1974, and starting down the presidential primary trail again in 1976.

But his wheelchair and increasingly evident deafness served as a handicap to his personal communication with his once-ardent following. After losing to Jimmy Carter in Florida, Wallace's hopes were ended.

His second marriage ended in divorce in January and a month ago Wallace allowed himself a rare public confession of his physical dependence when he asked the Alabama Legislature to vote him funds for two state troopers - who could move him from bed twheelchair and back for the rest of his life.