SANTIAGO, Chile (AP) _ The Supreme Court has ordered a military court to immediately reopen the investigation into the 1976 car-bomb assasination in Washington of former Foreign Minister Orlando Letelier and an American aide.

The court's unanimous decision Tuesday follows the recent disclosure of the identity of a women who allegedly was involved in the murder plot.

The woman, Luisa Lagos, was quoted by a local newspaper as saying she is a former agent of Chilean secret police, known as DINA, and that she traveled to the United States in 1976 under the assumed name of Liliana Walker.

The Supreme Court ordered the military court that handled the case before it was closed to question the woman, who has been under police protection at an undisclosed location since going public last week.

The woman said she went to the United States with a DINA agent who prepared the Letelier killing.

Letelier and an American aide, Ronni Moffit, were killed Sept. 21, 1976, when his car was destroyed by a bomb in downtown Washington.

Letelier was a prominent foe of the Chilean military regime of Gen. Augusto Pinochet. The new civilian government of President Patricio Aylwin, who succeeded Pinochet on March 11, has promised ''full cooperation with the courts'' in the case.

The lower house of Congress on Tuesday unanimously approved a goverment- propo sed bill for the posthumous restoration of Letelier's citizenship.

The Pinochet regime had stripped him of citizenship two weeks before his death, accusing him of ''actions against the interests of the Chilean nation.''

Three Chilean army officers, members of the Pinochet regime's secret police, were indicted in the case by a court in Washington, but the Chilean Supreme Court turned down a request for their extraditions in 1979.

One of the officers, Maj. Armando Fernandez Larios, slipped out of the country in 1987 and surrendered to U.S. courts, where he admitted to a collaborative role in the plot to kill Letelier.

Fernandez is now living in the United States under a new identity after serving a seven-month sentence. The others, retired Gen. Manuel Contreras Sepulveda, who was the director of DINA, and his top aide, retired Col. Pedro Espinoza Bravo, are still in Chile.

The United States goverment, which repeatedly complained of what it called lack of cooperation by the Pinochet regime in investigating the assasination, has insisted that Contreras and Espinoza be tried, either in Chile or in the United States.

Contreras and Espinoza have said they were not involved in the case.

Another DINA agent, Michel Townley, an American, was convicted in the case in the United States and is now living there under a new identity after serving a jail sentence.

Two weeks ago, another alleged participant in the plot, Dionisio Suarez, was arrested by the FBI in Florida. Suarez, an anti-Castro Cuban, faces trial in Washington.

The U.S. ambassador, Charles Gillespie, discussed the Letelier case Tuesday with Interior Minister Enrique Krauss. After the hourlong meeting, Gillespie said he sees ''a strong will in the new goverment to investigate the case.''

Letelier's sister, Fabiola Letelier, a lawyer, called the court's decision Tuesday ''a positive step.'' However, she said, the family still wants the case transferred from the military court to a civilian court.