The conservative congressman from Rockford, Ill., wanted to talk that Friday morning in April 1968. The night before, Martin Luther King Jr. had been gunned down in Memphis. Outside the congressman's office, the city of Washington was in flames.

"I haven't told anybody this," he confided to two visitors from his home district. "I've decided to vote for the open-housing bill."

For Rep. John B. Anderson, it was a bold step that could have led to political extinction back home. Instead, it launched a national political career.

Twelve years later, the voters of Massachusetts and Vermont discovered him and, by giving him strong second-place finishes in their primaries, turned him into the new matinee idol of the 1980 campaign.

Today he carried his euphoric campaign to an appropriate place: Yale University, the birthplace of "Doonesbury," the cartoon strip that took a liking to the Illinois Republican when everyone else was ignoring him.

More than a thousand people crowded into historic Battell Chapel at Yale to cheer the new hero of the young, the independent, the disaffected Democrats and other voters still looking for a home this year. Another thousand were turned away.

Referring to George Bush's remark that Anderson's showing Tuesday was "a freak occurence," Anderson addressed the Yale students with: "My fellow Anderson freaks."

The students cheered him when he said he was opposed to the draft and considered inflation as the nation's No. 1 problem. "You can become the foot soldiers to bring new ideas to America," he told them. "I believe in the power of ideas. That's the romance, the excitement of this campaign."

If Anderson's exuberant followers think of themselves as a political cult, they've gathered around a most unlikely guru.

He was raised in a deeply religious, conservative family in northwest Illinois, an experience that helped shape his political transformation in the last decade. He came to Congress in 1961, the successor to an immensely popular and powerful politician, Leo Allen, and fit comfortably into the conservative mold. In his first years in Congress, he voted against most of the progressive legislation offered up by Presidents Kennedy and Johnson.

But the civil rights revolution and the war in Vietnam began to turn him in a new direction. "Anyone who looks back at the decade of the '60s realizes we were undergoing social upheaval," he said some years ago. "The whole atmosphere began to register itself on my conscience. It began to convince me that times had changed, and that some of us -- grudgingly -- were going to have to change."

The open housing bill in 1968 offered him the opportunity to express those feelings, publicly, and the Kerner Report on rioting in U.S. cities prompted him to do it. "It was such a thorough documentation of the noose we had put around our cities that I didn't see how anyone could vote against the bill in the face of all that evidence."

It was his vote that sprung the bill from the House Rules Committee and his eloquence that helped pass it on the house floor.

From then on, he staked out an increasingly independent position in his party, and also rose to the No. 3 ranking job in the House Republican hierarchy.

Until Tuesday night, his campaign for the presidency was a lonely struggle to be heard. His strategy was to be different.

He courted blacks by stressing civil rights. He courted women by supporting the Equal Rights Amendment and advocating "freedom of choice" on abortion. He called for ratification of the strategic arms limitation treaty (SALT II), and opposed the MX missile and President Carter's call for a 5 percent real increase in defense spending.

He staked out a tough position on weaning America from foreign oil by recommending a 50-cents-a-gallon tax on gasoline, coupling that with a 50 percent reduction in Social Security taxes.

The opposes wage -- price controls, and favors a statutory ceiling on federal spending linked to the gross national product.

If Anderson is the new matinee idol of the campaign, his image-makers have some work to do. Yesterday morning there were two network camera crews waiting at Boston's Logan Airport when he arrived for his flight to New Haven.

The white-haired candidate got out of his car, walked quietly through the passive crowd and slipped into the terminal. Suddenly the cameramen did a double take. "Hey, was that guy Anderson?" one shouted. And, in a flash, they turned on their floodlights and chased after the man of the moment, for the moment.