Gov. James R. Thompson (R) today declared victory in the closest governor's race in the 1982 elections after complete, though still unofficial, returns put him approximately 9,500 votes ahead of Democrat Adlai E. Stevenson III.

But Stevenson refused to concede, and his campaign aides said he would begin assembling a transition task force at his farm in Hanover, Ill., Saturday. "We consider ourselves the governor-elect," said his campaign manager, Joseph Novak.

"No one wants this election count over more than me, but the people are entitled to their choice, and at the moment no one knows who that is," Stevenson said.

He said he was preparing for a transition "under very difficult circumstances."

The Stevenson camp's hopes were pinned on finding enough discrepancies in the official Cook County precinct-by-precinct canvass to reverse the outcome. A canvass is a normal review that occurs in each of the state's 102 counties after every election. It has already been completed in more than half the counties, but in Cook County -- which includes Chicago, where Stevenson won 72 percent of the vote -- it is expected to take until next Wednesday.

Thompson said at his victory speech that he believed canvass results from the entire state will give him a margin of between 10,000 and 11,000 votes.

"This is a substantial victory," the governor said at the traditional victory news conference. "We will not let them take it away from us."

Actually, it was anything but substantial. If the current figures hold (various tabulations today had Thompson anywhere from 9,182 to 9,922 votes ahead), Thompson will have won by a margin of less than one vote per precinct, or roughly .2 percent.

Each camp accused the other today of bluffing about their certainty in the final figures as the election count drama unfolds. Novak said that Thompson, by "prematurely" declaring victory, was setting himself up to later claim that the final results were "tainted."

Democratic party leaders said figures turned in to them on election night by Democratic precinct workers in polling places all over the state showed Stevenson the winner by several thousand votes. They did not produce a detailed tally sheet, however.

Thompson supporters--and a number of neutral observers--suggested that the real bluffing was coming from the Democrats.

Vote totals usually change during the canvass procedure, but unless there has been some distinct pattern of irregularity, these changes are normally small, and often balance each other out.

"The canvass is not going to produce any significant change," said Robert Barr, GOP chairman of Cook County. While many observers believe that a swing of more than 9,000 votes in the canvass was unlikely, the Stevenson forces took heart from new reports today that more than a dozen Chicago precincts had turned in results showing a zero vote total for Stevenson.

There was no official explanation for these totals, but it is so extremely unlikely that a precinct in overwhelmingly Democratic Chicago would fail to produce a single vote for the Democratic nominee that Stevenson supporters believed there must be major errors in the tallies.

In the canvass, election officials from each county provide party leaders with their unofficial precinct-by-precinct returns. The party officials then compare those figures with the figures they received from their poll watchers on election night. If there is a discrepancy, it is resolved in a hearing before election commissioners.

Once the county-by-county procedure is completed, returns are submitted to the state board of elections. By law, it must make the results official and declare a winner by Nov. 22.

Once a winner is declared, the loser has two options. If he has achieved 95 percent of the vote total of his opponent -- a certainty in this case -- he can demand a recount.

The recount, which costs the petitioner $10 per precinct, is not designed to provide a new statewide tally. It is limited to 25 percent of the precincts in the state--precincts that the petitioner may choose himself. It is designed to provide information that the loser may use in a lawsuit to challenge the outcome of the election.

Such a suit would go directly to the Illinois State Supreme Court, which would appoint a three-judge panel to hear it. If the panel finds the case has merit, it can order a complete recount or even a new election -- although neither step has ever been taken in a statewide election in Illinois history.