A federal grand jury here has indicted seven persons, who described themselves as members of a secret communist organization, in the 1983 bombing of the U.S. Capitol and seven other bombings in the District and New York City, prosecutors announced yesterday.

The five-count indictment, returned last month and unsealed yesterday in U.S. District Court, charges that the seven sought to change federal policies through what they called "armed propaganda."

Six of the seven are already incarcerated, serving time for, among other things, participation in a 1981 Brink's armored truck robbery, weapons possession and the use of aliases. The remaining member charged yesterday is a fugitive.

The Nov. 7, 1983, bomb blast at the Capitol, which caused $265,000 in damage, ripped through a conference room near the Senate chamber and the offices of then-Minority Leader Robert C. Byrd (D-W.Va.), and shook the Capitol grounds in what some witnesses described as sounding like a sonic boom.

The indictment also charges that the seven were responsible for similar attacks at the Naval War College at Fort McNair, in 1983; the Washington Navy Yard's computer center, in 1983, and its officers club, in 1984; the FBI office in Staten Island, N.Y., in 1983; the Israeli Aircraft Industries Building in New York, in 1984; the South African consulate in New York, in 1984, and the Patrolmen's Benevolent Association in New York, in 1985.

Moreover, the indictment charges that the organization, operating under such names as the Revolutionary Fighting Group, the Armed Resistance Unit and the Red Guerrilla Resistance, was planning attacks at seven other sites in the Washington area, Maryland and Delaware, including a D.C. law firm, the U.S. Naval Academy in Annapolis and the Old Executive Office Building in downtown Washington.

In a statement accompanying the indictment, U.S. Attorney Jay B. Stephens said: "Let this be a warning to those who seek to influence the policies of the United States government through violence or terrorism that we will seek unrelentingly to bring them to justice. Those who attack our sacred institutions of government and seek to destroy the symbols of our democratic system ultimately will have to pay the price."

Stephens singled out various law enforcement agencies and two prosecutors in his office, Ronda C. Fields and Margaret Ellen, who handled the case, for praise in the statement.

Some of those charged in the indictment had been suspected in the Capitol bombing for some time. Charged yesterday were: Laura Whitehorn, Linda Evans, Marilyn Buck, Susan Rosenberg, Elizabeth Duke, Timothy Blunk and Alan Berkman.

No one was injured in the bombing at the Capitol, which took place about 11 p.m., moments after a telephone call was made to The Washington Post, warning that a bomb had been planted.

A tape-recorded male voice identified himself as part of the "Armed Resistance Unit" and said the bombing was in support of the struggle against American military aggression, in response to "Grenada and Lebanon." At the time, U.S. marines were dug in at the Beirut airport in Lebanon and American soldiers had recently invaded Grenada, routing Cuban forces.

A communique from the group apparently mailed to a local radio station just after the bombing stated in part: "{W}e purposely aimed our attack at the institutions of imperialist rule rather than at individual members of the ruling class and government. We did not choose to kill any of them this time. But their lives are not sacred . . . . "

The 23-page indictment depicts a group bent on violently altering the course of government policy, and virulently opposed to arms manufacturers and the Israeli and South African governments.

The indictment says that in May 1985, Buck, Whitehorn and Evans had stashed in Baltimore a file labeled "In Progress" that contained photographs, "handwritten surveillance notes" and documents related to potential bombing targets.

According to the indictment, members of the group, operating out of Connecticut, New Jersey, Pennsylvania and Maryland, commonly had on hand hundreds of pounds of explosives, including blasting caps, dynamite, detonating cords and ammunition, plus bulletproof body armor and high-powered handguns and semiautomatic weapons.

Rosenberg, 32, and Blunk, 30, were sentenced together in May 1985 to 58-year sentences for possession of 12 guns and 600 pounds of explosives. Rosenberg also is a suspected member of the Weather Underground, the 1960s radical group.

Buck, who is in jail, was convicted yesterday in Manhattan in the Oct. 20, 1981, Brink's armored car robbery in Rockland County, N.Y., in which a guard and two police officers were killed. A federal court jury there found Buck, 40, and Mutulu Shakur, 37, guilty on eight counts, which included racketeering, conspiracy, armed robbery and murder in the Brink's robbery and a string of other robberies in New York and Connecticut.

Evans, 41, was sentenced to 40 years in prison in May 1987 for buying guns illegally in the New Orleans area in 1983. She already was serving a five-year sentence for two other federal convictions.

Whitehorn, 30, who also has been linked to the Brink's robbery in New York, has been tried and convicted on charges of making and possessing false identification documents and possession of weapons.

Duke, 47, fled while awaiting hearings in Philadelphia in 1985 on charges of possessing explosives and illegal weapons. She was considered armed and extremely dangerous, and is still at large.

Before she became a fugitive, Duke had been arrested with Berkman, 42, a physician, in 1985. He was convicted in 1987 on charges of possession of illegal weapons, explosives and false identifications. He is serving a 10-year sentence.