A summer intern's tongue-in-cheek reply to a letter written to Rep. Max Baucus (D-Mont.) has kicked up a mighty ruckus and become one of the liveliest issues in this year's Montana senatorial race.

Aides to Baucus, who is running for the Senate seat held by Democrat Paul Hatfield, want to laugh the whole incident away as a bad joke.

But Larry Williams, Baucus' Republican challenger, refuses to let it die.

It all started last summer, when Missoula Life Insurance salesman Steve Kuburich wrote Baucus a light-hearted letter with a serious message - the Social Security system should allow workers to opt out and put their money into annuities instead.

After outlining his ideas in a letter addressed to "Dear Max," Kuburich signed off, "Anyway, Max, you need a chuckle for the day. Keep up the good work."

An intern in Baucus' office, Rick Fijolek, was in charge of answering letters about Social Security.

"While I took the letter seriously, I felt that the response could be humorous without being misperceived," Fijolek said later. Thinking Kuburich was a personal friend of "Dear Max," the intern wrote a tongue-in-check reply that began, "You're right, Steve, I do need a chuckle a day."

A paragraph later came the punch:

The IRS people are very nice," Fijolek wrote in Baucus' reply.

"They allow every representative to send in the names of 20 people and then they audit these people. You see, the people at IRS understand that we get a lot of ridiculous letters from our constituents and want to help us get a few of them off our backs, so to speak . . .

"One of my staff saw your letter and figured you were a real crackpot. What can I say except that I'm sorry? I figured I'd warn you so you could get your files in order."

Kuburich didn't laugh, and neither did Williams, a commodities broker who trails Baucus by a wide margin in their Senate race.

Two weeks ago Baucus held a press conference to air the correspondence. Despite a later letter from Baucus that answered Kuburich seriously, Williams said he was asking the Justice Department to investigate whether such an Internal Revenue Service quota really exists and demanded that Baucus explain the incident.

Stephen Browning, administrative assistant for Baucus, said "this entire episode was a staff error" and accepted full responsibility, but that didn't satisfy Williams.

"There are a lot of questions still unanswered," Herb Williams, a political consultant to Larry Williams' campaign, insisted yesterday. He said the letter would be used to generate voter support, but refused to say how because he wants to "surprise" Baucus.

Montana newspapers carried extensive accounts of Williams' press conference Aug. 8, and of Browning's reply on Aug. 10.

Editorial reaction was mixed.

"Sorry, Max, but I just can't laugh this one away," said the Tribune-Examiner in Dillon.

But the Montana Standard - Butte Daily Post said the reply letter "was obviously a joke" and warned that unless candidates tolerated a little levity "political campaigns in Montana would go from almost unbearable to absolutely."

One veteran of Montana politics said the incident was "a tempest in a teapot" drummed up by Williams in a desperate effort to catch Baucus.The two-term congressman led 48 to 30 percent in a poll earlier this summer.

Meanwhile, Kuburich is still nursing hurt feelings and waiting for an apology from Baucus' office.

Fijolek, who is working this summer for the Democratic National Committee, is hoping the whole issue is soon forgotten.