WASHINGTON — The U.S. Supreme Court heard oral arguments Tuesday in a constitutional dispute that goes back to 1986, when former Maine Gov. Joseph E. Brennan stopped 50 Maine National Guard personnel from participating in a Pentagon training exercise in Central America.

The case pits the governors of Minnesota, Maine, Iowa, Montana, Ohio, Massachusetts and Vermont, who claim the dispute is a “states’ rights” issue, against the federal government and the governors of 29 other states, who argued that the dissident governors are “seeking to arrogate to (themselves) a role in foreign affairs.”

A decision by the justices is expected by July. The verdict will clarify a murky portion of the U.S. Constitution regarding the shared authority of the states and federal government over the nation’s military reserve units.

There is no disagreement on that issue between Brennan and Gov. John R. McKernan, even though they will be political opponents in this year’s gubernatorial campaign.

Both said that the Constitution leaves to the states the final say over deployment of state Guard personnel. Pentagon attorneys contended that Guardsmen automatically submit to federal status when they go on training exercises, which are financed by Pentagon dollars.

As a member of Congress, McKernan voted against an amendment sponsored by Rep. G.V. “Sonny” Montgomery, D-Miss., that stripped governors of the power to block Guard training missions. The amendment was adopted in 1986 after Massachusetts, Minnesota and nine other states followed Brennan’s lead and blocked Guard training missions in Central America.

Lower federal courts have ruled both for and against the dissident states’ position on Guard deployment. The high court agreed to review a lawsuit filed by Minnesota Gov. Rudy Perpich challenging the law, and Maine Attorney General James Tierney filed a brief supporting the Minnesota suit.

John Tunheim, chief deputy attorney general for Minnesota, asserted that the Constitution entrusts the power to train militiamen to the states, and that power includes the question of where they will be trained in peacetime.

Solicitor General Kenneth Starr said that federal law and the Constitution provide that National Guardsmen wear “two hats” as a result of their dual status as members of the state and federal reserve forces.

Starr said that when they are activated for training exercises, Guardsmen are members of the federal forces and that states, therefore, have no say in where those exercises take place.

Tunheim said that the founding fathers created state militia because they “greatly feared the effect of a large standing army.”

“They believed that state control would be a very important check on the federal government,” he said.

During Tuesday’s oral arguments, several Supreme Court justices seemed to lean toward the Pentagon’s position.

“All you’re complaining about is that you want the (federal) money without being subject to training orders,” Justice Antonin Scalia snapped back at Tunheim following one long exchange.

Justice Anthony Kennedy expressed concern that according to the Minnesota lawsuit, the federal government would be unable to train reserve personnel “for some of the things we’d call them up to do.”

The National Guard has been under dual state and federal control since Congress made it a component of the Army in 1933. Enlistees enroll simultaneously in the state militia and a reserve unit of the U.S. armed forces.

The dual-enlistment system “worked very well until governors decided to play a role on the stage of foreign policy,” Starr said.

The Army National Guard provides 46 percent of the Army’s combat units and 28 percent of its support forces.

The Air National Guard provides 73 percent of the nation’s interceptor forces, 25 percent of the tactical fighter aircraft and 24 percent of tactical air support.

While governor in January 1986, Brennan ruled that it was “unsafe” to send Maine citizen soldiers to Honduras. Approximately 6,000 troops from reserve units in 30 states were scheduled to participate in the massive training exercise.

Eleven other governors, most of whom opposed President Ronald Reagan’s military policies in Central America, followed Brennan’s lead and withheld permission for their Guard personnel to train in that region.

Among them was Massachusetts Gov. Michael Dukakis, who filed a suit challenging the Pentagon’s authority over Guard deployment. Dukakis authored a plank in the national Democratic Party platform claiming that Reagan had used the Guard training programs to “intimidate” Nicaragua and to provide back-door help to the U.S.-funded Contra guerrillas.

Pentagon officials termed the governors’ revolt a “dagger pointed at the heart” of America’s military readiness.