A D.C. Superior Court judge has dismissed an assault and rioting indictment against 17 members of the Revolutionary Communist Party, upholding their charge that the indictment resulted from government vindictiveness after police clashed violently with party demonstrators near the White House last winter.

In a four-page order issued Wednesday, Judge Carlisle E. Pratt held that government prosecutors failed to correct indictment procedures that he had found earlier were "motivated by vindictiveness," thus justifying the dismissal.

The 17 demonstrators originally were charged in two separate indictments with 15 assault and riot counts against one group of defendants and 11 counts against the other.

Defense attorneys asked that the two indictments be merged. In response, the demonstrators were reindicted in a single indictment but with all the counts in the original separate indictments levied against all 17 defendants.

This had the effect of making the defendants "vulnerable" to many additional counts, Pratt said, with potential prison sentences increased by 135 years and fines by $5,000.

Though prosecutors denied this amounted to vindictiveness, they failed to show they were not so motivated, Pratt held. In addition, he said, prosecutors in the U.S. Attorney's office failed to take other remedies suggested by Pratt such as quashing counts in the reindictment "so that each defendant would maintain the same vulnerability to charges and penalties that he or she did in the original indictments."

Asst. U.S. Attorney Mary Ellen Abrecht, who has headed the prosecution of the case from the beginning, said yesterday the government will appeal Pratt's ruling.

Russell F. Canan, one of six defense attorneys in the case, called Pratt's order a "right and necessary decision."

Revolutionary Communist Party spokeswoman Sharon Payley called the ruling a "major tactical retreat" by the federal government.

The indictment grew out of a wild rock-and-bottle-throwing melee on Pennsylvania Avenue near the White House last Jan. 29, during the state visit of Chinese Vice Premier Deng Xiaoping.

Some 400 party members and supporters, who were protesting the visit, battled briefly with helmeted police after the demonstrators charged into Lafayette Square, hurling bottles, sticks, lead fishing weights and other objects at officers massed on Pennsylvania Avenue.

Police counterattacked, charging on horseback and on foot. Reporters at the scene observed both demonstrators and police clubbing each other with sticks and batons. More than 50 persons were injured, and 78 arrests were made.

The Revolutionary Communist Party is a small militant organization that predicts there will be a mass uprising and armed overthrow of the PRESENT U.S. government in the 1980s.

Estimated by competing leftist groups to have 1500 to 2,300 members nationwide in 1976 and considerably more now, the party supports a strict form of Maolism. It opposes the present Chinese regime's "revisionist" policy of developing trade and economic ties with the United States and other capitalist countries. Members contend this will re-open the way to capitalist domination of China.

Throughout pretrial maneuvering this fall, party activists contended the government was attempting to "railroad" the 17 indicted demonstrators, including party chairman Bob Avakian, by piling on multiple counts in the indictment.

Prosecutors denied this and maintained that all the defendants could be held as "aiders and abettors" for each individual assault or other crime since all were "knowing members' of a mob that intended to instigate a violent encounter with police.

Abrecht and other prosecutors also argued that the additional counts in the reindictment would add little or no penalty since defendants convicted as aiders and abettors, rather than as principals, customarily receive concurrent sentences on counts involving the same general incident.

Pratt rejected this argument, however, and said the demonstrators were "nevertheless" prejudiced by the reindictment."

Jubilant party activists say they plan more protest actions here and elsewhere. Led by the feisty Avakian, 36, the organization employs militant rhetoric and demonstration tactics but says it opposes individual acts of terrorism, like those of the Red Brigades in Italy.

They steadfastly deny initiating violence at the White House demonstration last Janurary. Violence, Avakian says, will come later, when the "masses of this country rise up overthrow capitalism," sometime in the 1980s.

In the meantime, he said, the party will continue to stage legal demonstrations.

"We know the difference between a demonstration and a revolution," he said in a recent interview. "Revolution is definitely illegal, and we will not apply for a permit for it."