Walter Mondale looks stronger with each passing day. The former vice-president - winner by a 41-to-35 percent margin in Illinois - warned his supporters that there's still a ''long road to the convention.'' But political analysts called Mr. Mondale's victory here over Gary Hart solid and impressive.
Senator Hart now approaches the huge and potentially decisive New York primary in two weeks at a substantial disadvantage.
Three aspects of the Mondale triumph in Illinois were particularly notable:
* Mondale rolled up a solid lead over Hart, even though Jesse Jackson got 70 percent of the black vote. Most of Mr. Jackson's black support would have gone to Mondale if this had been a two-man, Hart-Mondale contest, analysts say.
* Mondale won ''pulling away.'' Exit polls by ABC-TV found that voters who picked their candidate in the final two days were choosing Mondale over Hart by a margin of 4 to 3. A week before, voters in Illinois had been gravitating toward Hart by a 2-to-1 margin.
* Mondale held his union support. In some earlier states (New Hampshire, Massachusetts, Florida), Mondale lost rank-and-file union voters to Hart, even though he had the backing of union leaders. In Illinois, the union lines held, and Mondale took that vote 39 to 28.
Despite his victory here, Mondale quickly dismissed talk that he has regained his ''front-runner'' position. He lost that title unexpectedly three weeks ago after defeats in New Hampshire, Maine, Vermont, and Wyoming.
While Mondale may be reluctant to reclaim the mantle of front-runner, Illinois showed that Mondale - and not Hart - is once again the man to beat in the Democratic race.
Further, the Illinois victory will make Hart's task even harder. Money and volunteers are drawn toward winners, not second-place finishers. Illinois will make it that much more difficult for Hart to regain his momentum as he moves east for three weeks of head-to-head campaigning against Mondale in Connecticut (March 27), New York (April 3), and Pennsylvania (April 10).
These are all known, in political terms, as ''media states.'' They are too densely populated, and there is too little time left, to conduct the kind of person-to-person effort that worked for Hart in New Hampshire. Successful campaigning in media states requires a fat wallet to buy TV ads in those extremely costly markets. There is little expectation that Hart will be able to buy the amount of air time he needs to run a comprehensive campaign in all three states.
A few weeks ago, Hart strategists felt they could make up for their lack of funds with free media coverage - news reports in magazines, in newspapers, and on TV and radio - which would keep the senator's face and name prominently before the public.
That has not quite worked the way it was supposed to. At first, after New Hampshire, Hart's face smiled out from the covers of Newsweek, U.S. News, and other publications. He was a subject of media and public fascination for a span of about two weeks. But in recent days, much of the ''free'' media has turned sour. Hart's miscues have made headlines. The media wave that once pushed Hart so quickly ahead finally broke, and Hart found himself caught in the undertow here in Illinois.
The young senator attempted to put the best face on his defeat.
''I think Vice-President Mondale had substantial advantages in Illinois,'' Hart said. He pointed to ''both organized-labor support as well as political-institution support, particularly in the city of Chicago, and they both performed for him very well.''
What Hart did not say was that Mondale will have those same advantages - labor and Democratic leaders - in the New York contest. New York is labor's strongest state, and most of the top Democratic politicians there are lined up behind Mondale.
Here in Illinois, the voting showed that such coalition politics still works.
From the beginning, Mondale has courted just about every segment of the old Franklin D. Roosevelt coalition: labor, blacks, Southern whites, big-city residents, foreign-born voters. And here in Illinois, the old coalition came through.
Specifically, Mondale ran strongly with traditional Democrats, including Roman Catholics, union members, low- and middle-income families, Hispanics, and most of the blacks who didn't go with Jackson. It was just the kind of pulling together that Mondale's advisers hoped to see before their candidate goes into New York and Pennsylvania, where such coalition politics has also been successful in past years.
While most eyes here were focused on the popular vote, Illinois also pushed up Mondale's tally of convention delegates. Illinois added 97 delegates to his total, and raised his nationwide delegate strength to 639. That is nearly one-third of the 1,967 needed for nomination.
Hart garnered 39 here, and nudged his total to 381. Jackson didn't win any Illinois delegates, despite getting 21 percent of the vote. But his political ally, Chicago Mayor Harold Washington, picked up 35 delegates as a ''favorite son'' candidate, and those votes could eventually find their way into Jackson's column. Jackson has 72 delegates from earlier primaries and caucuses.
Computer analysis of the vote in Illinois showed many of the same patterns detected in earlier primaries.
Once again, Mondale did best with older voters, with hard-core Democrats, and those with lower levels of education. People liked him most of all because of his experience in government.
Hart attracted more young voters, independents, and college graduates. He was most liked for his independence and his promise to bring change.