HELENA, Mont. - The government admitted yesterday that some of its agents have leaked confidential information about the Unabomber case, but argued that the misbehavior was not significant enough to let suspect Theodore Kaczynski go free.

Meanwhile, in Chicago, a woman who worked with Kaczynski almost 20 years ago said Thursday that they dated only twice - and she rejected any suggestion that the abortive romance somehow sparked the Unabomber attacks.

Ellen Tarmichael also confirmed reports that after she broke off the relationship, Kaczynski harassed her by posting limericks about her at the packing material plant, prompting his younger brother, David Kaczynski, to fire him on Aug. 23, 1978.

''Further speculation that my limited involvement with Ted Kaczynski somehow resulted in the acts of terrorism attributed to him would be grossly unfair,'' she said, adding that the first bomb from the Unabomber was sent ''almost a month before I ever met Ted Kaczynski.''

Kaczynski, 53, was arrested April 3 at his Montana mountain cabin.

He is jailed in Helena, charged only with possession of bomb components and not with any of the Unabomber attacks, which killed three people and injured 23 in nine states.

Kaczynski's court-appointed lawyer, Michael Donahoe, claimed that a flood of leaks from unnamed federal sources has ''poisoned the entire population of grand juries within the United States against Mr. Kaczynski.''

Donahoe asked that Kaczynski be freed, the lone charge against him dropped and any further prosecution barred. He also asked that everything taken from Kaczynski's Montana cabin be returned to his client.