The neat Illinois alignment of rank-and-file Republicans for Ronald Reagan and party establishment chieftains for John Connally in the first big state primary March 18 has been shattered, with defections from both camps streaming toward George Bush.

Ever since Connally's dismal fourth place in the Iowa caucuses Jan. 21, the party leaders who leaped aboard his bandwagon a year ago have been perched to jump off -- with Bush as theprobable landing place. That's no surprise. What's unexpected is the quick post-Iowa shift at the grass roots toward Bush, as revealed by Reagan's own polls.

But doubt persists here about Bush's ability to handle his new eminence. Furthermore, his organization is still in its formative stages and sponsors no candidates filed for delegate to the Republican National Convention. His spectacular rise here is based on the crashing impact of Iowa on ancient Republican animosities in this state.

Following the old adage that all politics is local politics, the struggle here is for control of the Illinos Republican Party rather than any mere presidential nomination. State Rep. Don Totten, Reagan's hard-nosed state chairman, is fighting Gov. James Thompson on a wide front involving sate legislative issues and intraparty control.

Totten made clear last year that if his Reaganites controlled the Illinois delegation, the governor would not go tothe national convention as its chairman. That guaranteed all-out war with Big Jim Thompson, whose ego rivals his 6-foot-6 stature. His allies in the legislature and party structure picked Connally as the most promising stop-Reagan candidate.

Second thoughts set in when Connally's politically disastrous Mideast speech offended Jewish Republicans here. Third thoughts arrived when Connally finished a poor second in last November's Florida preferential convention after privately promising Illinois backers a near-win. After Iowa, Connally's big names were ready to jump -- Bush.

The tip of the iceberg is Robert Hanrahan, a former Chicago congressman who surfaced last year as a member of Connally's "national advisory" committee but recently filed as a self-starting delegate candidate pledged to Bush. More important, Connally backers are staying put for now. But unless Connally scores an upset in South Carolina on March 8 or in Florida on March 11, they will abandon ship.

Until last week, it made little difference to the Reagan organization whether the big boys were for Connally or Bush. Reagan was a prohibitive favorite to win the Illinois preferential primary (or "bearty contest"). Reagan slates entered in 23 out of 24 congressional districts (opposing the regular party slates in 10 districts) figured to do well, even though Thompson's forces changed the primary to remove presidential preference designations from the names of delegate candidates.

Bush's Iowa upset made little difference to the Reaganites, spiritual heirs of Illinois grass-roots conservatives who stuck with Robert A. Taft to the bitter end in 1952 and led Barry Goldwater's hard- core delegates in 1964. But such activists cannot control a state primary where better than 1 million votes are expected. To their horror, Reagan's men found a dramatic shift to Bush in their own statewide polling after Iowa. They admit they desperately need a win in New Hampshire Feb. 26.

Bush's agents are not pressing too hard (particularly on Thompson, who was not happy over a little too much pressure from Connally). George Kangas, a young insurance man who is party chairman in suburban Lake County, runs Bush's campaign with this motto: the light is in the window for everybody who does not want Reagan. Since Bush has no official delegate candidates of his own, he will embrace any who have no commitment.

Sales resistance to this soft-sell is persistent doubt whether Bush has what it takes. Influential Republicans were disturbed by Bush's truculent tone in a Los Angeles Times interview reprinted in the Jan. 27 Chicago Sun-Times, so unlike the masterful image conveyed by Bush's paid television commercials widely shown here.

Thompson is among the skeptical, a situation not changed by Bush's performance Jan. 29 at a governor's mansion dinner for him closed to the press. Thompson told us he was "impressed" with Bush but thought he was "a little tired" and did not fully explain his views on coal usage (a major economic question in coal-rich southern Illinois). The morning after the dinner, the governor privately told an aide: "i still have not found my candidate."

But Reagan will not even attend a governor's mansion dinner of the kind provided all other candidates, following the advice of Totten, who fears Thompson wants to "set up" Reagan for unfavorable comparison. Sen. Howard Baker's efforts here, as elsewhere, are very little and very late, run by a Thompson foe, former House speaker W. Robert Blair. Thus have the combination of Iowa caucus results and Illinois tribal rivalries built the Bush fire on the prairie.