The State Department yesterday accused the Soviet Union of failing to use its influence to halt the hijacking of a Pakistani airliner and strongly suggested that the Soviets may have helped it along.

Spokesman William Dyess, making the unusual public accusation, said, "I don't see how the Soviets can entirely escape responsibility for what took place" while the hijacked airliner was on the ground for seven days in Kabul, Afghanistan.

Dyess charged that the Soviet Union made "no serious effort" to end the hijacking "despite its predominant position in Afghanistan and the city of Kabul." The hijacking began in the air over Pakistan March 2 and ended Saturday in Damascus, Syria.

Moreover, Dyess strongly suggested complicity by either the Soviet or Afghan government, or both, by saying the hijackers received more powerful weapons after they forced the airliner to land in Kabul. "They arrived with pistols; they left with machine guns," Dyess charged.

The State Department spokesman also charged that, according to "eyewitness American accounts," all three hijackers stook outside the plane at one point in view of Soviet and Afghan security personnel "without any apparent concern for their own safety."

A Soviet Embassy statement rejected the charges as "crude and undignified" and "completely groundless."

A spokesman said the embassy had privately rejected the State Department's charges several days ago. In view of this, the public charge apparently has "no other aim but to make some propaganda mileage out of this human tragedy," the Soviet statement said.

The State Department's charges paralleled those made by Pakistani officials, including President Mohammed Zia ul-Hag, charging a "deep conspiracy" between the Pakistani dissident hijackers and the Afghan government. Unlike Zia, however, the State Department zeroed in on the Soviets as the ones responsible for Afghan government actions.

The U.S. statements suggested that the Afghan regime of Babrak Karmal sought to take advantage of the hijacking to force Pakistan to recognize its legitimacy.

Dyess charged that Afghan authorities "initially prevented Pakistani negotiators from contacting the hijackers," insisting instead that the negotiations be conducted through the Afghan government. Pakistan has refused to recognize the Babrak government, which was installed with the help of Soviet military power in December 1979.

State Department officials said the Soviets have usually opposed hijackings in strong terms, and thus they considered the Soviet attitude in this case all the more remarkable. According to Dyess, the Soviets did not publicly condemn the hijacking until 10 days after it began.

Asked for a possible motive, State Department officials said the Soviets might have welcomed additional trouble for the Pakistani regime headed by Zia, who has been uncooperative on Afghan issues and is considered likely to forge stronger ties with the United States in the Reagan administration.

The United States was in diplomatic contact with the Soviets five times about the hijacking of the Pakistani airliner, according to State Department sources. The last of these contacts apparently was the meeting late last week to complain about lack of cooperation by the Soviets.

The immediate cause of U.S. activity and concern about the hijacking was the presence of four Americans among those held hostage.

The State Department confirmed yesterday that one of them, Craig Clymore, is under indictment on drug trafficking charges. State said another, whose real name is Lawrence G. Lome, is an escaped Canadian convict traveling on a fraudulently obtained U.S. passport.

The State Department praised Syria for acting "highly responsible" in the hijacking and did not condemn Pakistan for making concessions to the hijackers, calling this "a very difficult decision."