A U.S. grand jury in Alexandria yesterday indicted a 32-year-old Washington taxi driver on charges of conspiring with an Islamic "terrorist organization" to violate U.S. firearms and bank robbery laws.

David Mitchell Powell, also known as Daud Abdar Rahman Abdallah, was charged with conspiracy in the illegal purchase of a cache of more than 20 weapons and commission of at least six area bank robberies in the spring of 1979.

Powell also is charged with conspiring to obstruct the administration of justice by planning to kill prosecutors who were investigating the group's activities, the indictment says. The four-count indictment also charges Powell with two counts of illegal aquisition of weapons and attempted bank robbery.

According to the indictment, Powell is a member of a group called the Islamic Guerillas of America (IGA), also called the Majurhareen Walauser, which was formed an undetermined time ago by Powell and six unindicted coconspirators to "prepare, train and indoctrinate its members and followers for worldwide religious warfare and revolution intended to spread the Islamic faith."

Powell allegedly was the head of one of the group's revolutionary cells. The IGA allegedly met at a Muslim mosque called Bait-Ul-Allah, in the 1200 block of Crittenden Street NW. Powell is charged with conspiring with the unindicted coconspirators to acquire weapons using false identification, rob banks and "prepare, train and indoctrinate . . . members and followers for worldwide religious warfare and revolution intended to spread the Islamic faith."

Law enforcement officials said they believe they have identified about 35 alleged members of the so-called IGA, some of whom are fugitives on firearms charges. Members of this group, law enforcement officials believe, work in the Iranian Interests Section of the Algerian Embassy, assemble caches of guns, hand out leaflets preaching violence, or otherwise engage in subversive activities aimed at opposing the U.S. government and other perceived enemies of Islam.

The indictment handed down yesterday was the result of a 1 1/2-year investigation by FBI and Alcohol, Tobacco and Firearms (ATF) agents. In it, Powell is alleged to have assisted the group's members in obtaining jobs as taxicab drivers to serve as a cover for their activities.

He and the unindicted coconspirators also are alleged to have arranged for weapons training for group members and to have planned to travel to prisons and penitentiaries in various parts of the United States to recruit new members and set up IGA networks.

The indictment also alleges that the conspiracy included plans to assist arrested members of IGA in making bail and fleeing the country. It is alleged that Powell recruited people to commit acts of "terrorism, including assassination."

The 12-page indictment contains a lengthy list of "overt acts" as part of the conspiracy, including the illegal purchase of shotguns, carbines, revolvers and magnum handguns from gun shops all over the Washington area, from Potomac Arms in Alexandria to Clark Brothers in Warrenton to Sears Roebuck in Baltimore, where several shotguns were purchased.

According to ATF agents, Powell was arrested at 7:55 a.m. yesterday at his 1446 Parkwood Pl. NW residence and is being held in the District of Columbia jail on $250,000 bond, after a hearing yesterday afternoon before U.S. Magistrate Arthur T. Burnett.

Of the six unindicted coconspirators, two of them, Musa Abdul Majid, 32, and John Leo Roberts, now are fugitives and are believed to be outside the United States, possibly in Iran. Three others, Morris Haywood Smith, Al Fletcher Hunter Jr., and Clarence Edward Griffin, are in U.S. prison on firearms violations. The sixth, Jimmie Franklin McEachern, is free on bond pending an appeal of a firearms conviction.

According to the ATF, Hunter testified two weeks ago at the murder trial of slain Iranian diplomat Ali Akbar Tabatabai that he had driven the getaway car after the murder.