A small corps of Michigan Democrats Saturday may provide the first insight into public reaction to the attempted rescue of the American hostages in Tehran. But it will be insight viewed through a glass, darkly.

The 30,000 or so veteran party activist who will choose between President Carter and Sen. Edward M. Kenndy at Democratic caucuses around the state have so many other things on their minds -- ranging from the national economy to local politics -- that it may be impossible to determine what impact the Iran news has on voting. At stake are 141 delegates.

Leaders of the Carter and Kennedy campaigns here said today that telephone canvassing indicates almost all the Democrats expected to attend the caucuses had picked their candidate before hit newspapers and television screens Friday morning.

Accordingly, both Joseph Crangle, the New Yorker who is running Kennedy's Michigan campaign, and Curt Wiley, the Iowan managing Carter's effort, guessed today that the mission may not have much influence on the results. But both emphasized that any such prediction was pure guesswork.

The unusual process here, though, seems likely to make local political and organizational loyalties at least as important as national and international affairs in the caucus voting.

The Michigan Democrats have done away with such traditional niceties as secret ballot, one-man one-vote, and free access to the polls.

Only 40,635 of the state's 6.5 million voters will be permitted to take part Saturday, and most of those had to pay a $10 fee. The two camps expect about 75 percent of those eligible to turn out. Those who do will ballot under a weighted scheme that could give some individuals, in effect, more than one vote.

And they will be asked to sign their ballots. Thurs, a Detroit party worker will cast his vote under the watchful eye of Mayor Coleman Young, the city Democratic kingpin and a strong Carter backer. Members of the United Auto Workers know that the union's leaders, most of whom favor Kennedy, will see how their members vote.

"I used to say it was ironic that a state as progressive as ours came up with this system," said Frank Kelly, the attorney general. "But ther more I looked at it I gave up on 'irony.' My new word is 'bizarre,'"

The system is also designed so that it is highly unlikely for either Carter or Kennedy to score an overwhelming win -- another factor that may mute whatever message Michigan has to send about the hostage rescue effort.

Under one line of analysis, the Iranian news might help Carter by taking attention away from the economy. Michigan is hurting badly because of sharp declines in automobile sales -- declines triggered in party by Carter's anti-inflation efforts. Kennedy hit hard on that point during his one day of campaigning here Thursday.

Analysts of a different pesuasion, however, point out that small electorate in the caucuses here will be made up of sophisticated political activists, the kind of people who might be least likely to be distracted from their primary concern by news of the moment.

Because neither campaign has any strong feeling for the impact of the Iranian development, both decided today that the best approach was to tread extremely lightly on the subject. Kennedy and Carter's chief stand-in, Vice President Mondale, both called off their scheduled campaign stops here today.

And both campaigns told workers to answer "no comment" when the press called to inquire about the rescue effort and its political effect.

That word did not reach Mayor Young, however, who was awakened by a reporter at 5:30 this morning and asked to comment.

The mayor said that Carter had done exactly the right thing. "We ought to get it on," he said, "at this point, [Carter] ought to find out whether the ayatollah is BS-ing."