Five environmental and disarmament groups are threatening to sue the U.S. Army if it tries to destroy Pershing missiles in Utah.

The Intermediate Nuclear Forces Treaty, which was ratified and delivered to the Moscow summit this week, requires the United States to destroy 698 Pershing Ia and II missiles within three years.The Army is considering four possible sites for the destruction. Two are in Utah: Tooele Army Depot and Hercules' Tekoi Test Range in Skull Valley. Other sites under consideration are at Pueblo, Colo., and Longhorn, Texas.

Rep. Jim Hansen, R-Utah, has said Army sources told him the Utah sites were out of the running. But that isn't enough assurance for Downwinders, Utahns United Against the Nuclear Arms Race, the Utah Environment Center, the Salt Lake Citizen Congress and the Utah Wilderness Association.

They wrote the Army that its recent environmental assessment of the impact of destroying some of the missiles in Utah was "thin in its content, flawed in its conclusions and improper - perhaps illegal - in its process. The Army has prepared this document in a vacuum, with no public participation."

The groups especially complained about a Nov. 24 test burn at Tooele, saying that the Army failed to adequately monitor drifting smoke from the test and failed to make public "scanty soil sample data" collected in the pit where the rocket was burned.

They said Utah is doing its share for the INF treaty by hosting Soviet inspectors at Hercules Bacchus Works despite security problems they present.

"If the Army selects a Utah site for Pershing missile elimination, the Army will have a great deal of explaining to do for the citizens of this state and before a federal court," the groups wrote.

Former U.S. Sen. Frank E. Moss was one of those signing the letter, representing Utahns United Against the Nuclear Arms Race.

State Sen. Frances Farley, D-Salt Lake, also issued a supporting statement. "I am very concerned about the impact on air quality that these missile burns would have. We already have very serious air pollution problems along the Wasatch Front, and I think it would be bad judgment to contribute to those problems by destroying the missiles here."

Steve Erickson, a spokesman for the military watchdog group Downwinders, called for Gov. Norm Bangerter to strengthen his position against Pershing destruction in Utah or said the Army could conclude that the state is willing to accept it.

Bangerter has objected to the Army destroying large numbers of missiles in Utah. He also earlier said Utah would not allow additional tests on destroying missiles until another state had also allowed a test. One such test was finally conducted this week in Pueblo, Colo.

Erickson attacked that test also, saying it was "nothing more than a public relations exercise. There is nothing new or significant the Army could learn from that test. The only purpose could be that the Army wants to reassure Coloradans that the missile burns are no big deal and to put pressure on Gov. Bangerter to reconsider his opposition to additional test burns in Utah."

Erickson said his group also disagrees with the Army that the November test burn in Tooele had "no significant impact" on the environment.

A Downwinders' statement said, "Complaints of difficulty in breathing, headaches and other irritations . . . were registered by several Utah residents over 20 miles downwind from the test burns.

"Observers of those tests witnessed a massive cloud that drifted into populated areas, greatly lowering visibility."