As word arrived that newspaper polls had made him the Republican favorite in the Illinois presidential primary, Rep. John Anderson won cheers from Bradley University students by seeming to abandon 15 years of staunch support for nuclear power.

Having just promised to answer questions "just as frankly and as honestly as I can," Anderson was greeted by the first questioner here inquiring about his position on nuclear power. Congressional colleagues had been predicting that Anderson's pro-nuke position ultimately would erode his feverish campus constituency. They did not reckon with Anderson's adroitness on the campaign stump.

He accused the Nuclear Regulatory Commission of failing to meet safety recommendations, adding that until it did, the government should "not grant new operating licenses." Cheers and applause. Criticizing President Carter's proposals for nuclear waste treatment, he declared: "I don't think that's good enough. If you can't do [better], then I don't think we should expand nuclear power." More cheers and applause. Nobody present would have doubted his anti-nuke credentials.

That is part of the pattern that moved Anderson from pathetic obscurity to darling of the national news media and now into contention as leading alternative to Ronald Reagan. Although depicted by admiring news accounts as the only candidate of principle, he tells audiences (mostly on college campuses) only what they want to hear and seeks confrontation only with his enemies. That is not quite St. John.

While deftly fogging his little-known nuclear past, Anderson plays to his collegiate audiences by attacking what he calls Carter's intention to "ultimately" draft men to "protect an [oil] interest that is vital" and by pushing the 50-cents-a-gallon gasoline tax that is remarkably popular on campus ("I love it, just love it," enthused an Anderson student booster at the College of Lake County).

In fact, his celebrated clashes with foes sketch less a profile in courage than a profile in political shrewdness, featured by his face-down of the gun lobby in New Hampshire. There has been more of the same in Illinois. He boosted the Equal Rights Amendment in Alton, home of anti-ERA crusader Phyllis Schlafly. When right-to-life pickets showed up outside Wheaton College, he opened his speech by proclaiming, "I square it [support of abortion rights] with my own Christian conscience." The audiences loved him.

This technique moved New England liberal voters out of Democratic primaries to support Republican Anderson. The difference in Illinois is that in addition, bona fide Republicans are turning to Anderson as the alternative to Reagan.

The process was explained to us by one state legislator, running as an uncommitted national convention delegate, who attended one Anderson speech. "All this business about ERA and abortion is hurting John," he said. "But when he gives conservative speeches like today about the balanced budget, he makes it easier for moderates to support him."

Whatever the impression given, however, Anderson is farther from the Republican main line on economic issues that on social questions. Even more abruptly than his softening on nuclear power, he has now totally abandoned his previous highly vocal support of broad-based tax reduction -- the principal economic strategy of his party.

Anderson's ravaging of Republican principles while sounding conservative is typified by his proposed budget revision, described in newspaper accounts as an example of Anderson the economic conservative. Actually, its proposed spending cuts of $11.3 billion are relatively insignificant and do not greatly disturb social welfare programs.

Anderson's adjustments on the revenue side are startling: $10.7 billion in revenue increases over and above the Carter budget's $49 billion in new taxes (which Anderson never mentions). Anderson's program even includes a one-year 5 percent surcharge on corporate profits.

Anderson would also slightly reduce the Carter defense budget that other Republican presidential contenders consider deficient. After disposing of the anti-abortion hecklers at Wheaton, he told the audience he would feel more comfortable with Sen. Edward Kennedy as president than with Ronald Reagan, and denounced Reagan's "total dependence on arms."

A candidate who comes over as high-taxation, anti-military, anti-nuclear and pro-abortion is understandably congenial to normal Democratic voters, who see him as more liberal than Jimmy Carter and more moral than Teddy Kennedy. That genuine Illinois Republicans have now made him the front-runner in their own party primary suggests that either they don't know what John Anderson stands for or in fact really stand for nothing themselves.