Sixty protesters facing possible jail terms for disrupting operations of the Rocky Flats nuclear weapons plant will invoke a novel defense today at their trial in Jefferson County court here.

They say the jury must acquit them of trespass and obstruction charges under Colorado's obscure "choice-of-evils" statute, which excuses criminal acts committed to avert imminent public danger.

The protesters, who for the past six months have been blocking railroad tracks leading to the plant, claim past and present radioactive emissions from Rocky Flats pose a severe health threat to Denver, 16 miles downwind.

Jefferson County prosecutors, who rested their case yesterday, have argued the protesters aren't entitled to the defense, which they claim applies ordinarily to imminent danger situations, as when a pedestrian trespasses to avoid the attack of an angry dog.

In the virtual absence of any guiding precedents, a ruling on the relevance of the choice-of-evils defense will come from Kim Goldberger, a 31-year-old county judge who sometimes wears a denim robe.

Goldberger announced yesterday he will at least hear the defense himself today - in open court, with the jury excused - before deciding if it can apply.

That, in itself, is a victory of sorts for the protesters, who've sought from the beginning to put Rocky Flats itself on trial.

The defense plans to parade before Goldberger several expert witnesses - including a noted British cancer researcher, Dr. Alice Stewart, and a former Atomic Energy Commission official. Dr. Karl Z. Morgan - to testify that low-level radioactive emissions from Rocky Flats imperil is neighbors and workers.

They also will present studies by Jefferson County Health Director Carl Johnson that they say show higher rates of cancer, leukemia, and birth defects among residents near the sprawling government complex than in neighborhoods farther away.

Operated for the government by Rockwell International Corp., Rocky Flats produces plutonium trigger devices for all U.S. nuclear weapons systems. Since it was built in 1951, the plant has had a number of accidents, which contaminated soil nearby with radioactive plutonium.

Almost 250 arrests have been made since last April 29, when the protesters, calling themselves the Rocky Flats Truth Force, set up their tent and teepee encampment among a rail link to the plant.

The trial began Monday for the first 60 protesters - 10 named defendants and 50 others who agreed to accept the jury's ruling.

Each defendant faces at least one charge of trepass and obstructing a passageway, misdemeanors punishable by up to six months in jail.

The most famous and oft-jailed member of the group, Dr. Daniel Ellsburg - the former Defense department analyst who leaked the Pentagon Papers - is charged with four counts of trespass and three of obstruction, and could get up to 3 1/2 years in jail if convicted.

Assistant district Attorneys Gay Guthrie and Steve Cantrell are trying to keep the issues narrowly defined. They killed a plan to move the trial to more spacious surroundings at U.S. District Court in Denver, claiming such a venue change would give "undue publicity to a misdemeanor, petty criminal trial."