Soviet authorities disclosed today that treason charges are being prepared against Anatoly Scaransky, a dissident who was arrested in March after a Soviet newspaper accused him of working for the Central Intelligence Agency.

The move raises the possibility of a spectacular show trial in which American diplomats and possibly journalists will be accused of recuriting dissidents for U.S. intelligence purposes. It was these allegations, attributed to a "repentent" dissident, that led to Scharansky's seizure.

A trial of this kind would pose a significant test of the Carter administration's resolve to speak out in defense of human rights in Eastern Europe.

Scharansky's parents received notification this morning that their son, 29, is being held for investigation under the treason statute, which carries a possible death penalty, friends said at a news conference. The family has not been permitted any direct contact with Scharansky since his arrest March 15.

The Soviets have not used treason charges against any dissidents since the trial in 1970 of 12 persons - 10 of them Jews - for plotting to hijack an airliner and fly it to Scandinavia. Two persons were given death sentences, but these were later commuted to 15 years imprisonment after an international outcry.

Scharansky, a computer specialist, applied to go to Isarel in 1973, but was turned down on grounds that his training had given him access to state secrets. Gradually he emerged as one of the boldest and most articulate dissident activists, serving as an informal spokesman for others Jewish "refusedniks," as those who have been refused permission to emigrate are called. q He was also a member of the unofficial group monitoring Soviet compliance with the 35-nation Helsinki document on European security, particularly its provision on human rights. That group has been a principal focus of a general Soviet crackdown on dissidents. Two other members - Yuri Orlov and Alexander Ginzburg - have also been arrested but the charges against them have not yet been specified.

At today's press conference remaining members of the Helsinki group - including retired Gen. Pyotr Grigorenko and Elena Bonner, wife of dissident physicist, Andrei Sakhrov - released a report intended for the Belgrade conference where compliance with the Helsinki accord is to be reviewed by the signatories. The Belgrade conderence opens June 15.

"The destruction of the Helsinki group on the eve of the Belgrade conference," concluded the report, "must be seen as proof of the refusal of Soviet authorities to fufill their human rights obligations and as a demonstration of readiness to severly punish those Soviet citizens who provide information about such violations."

The allegations against Scharansky were made by Sanya Lipavsky, a Jewish doctor who applied for exit permission but changed his mind. In an article in the government newspaper Izvestia and a later press conference to which only selected journalists were invited, he asserted that certain U.S. diplomats had enlisted Scharansky and several other "refusedniks" - including two who are still in Moscow.

Lipausky claimed that the diplomats used a mumber of CIA techniaues, such as mail drops, invisible ink, code names and material inducements to get dissident involved in a conspiracy aimed at betraying Soviet industrial and scientific secrets. He said that the dissidents often met with American journalists, the implication being that the reporters also encouraged subversive activities.

The only diplomat currently in Moscow alleged to be a CIA agent is Joseph Presel. Since publication of the articles, he has been followed everywhere and subjected to telephone harassment. Presl is a first secretary at the U.S. embassy, a career foreign service officer and a specialist in Soviet affairs.[TEXT OMITTED FROM SOURCE] but have not been arrested - to collect secret information.

The U.S. embassy has formally protested to the Soviets over the allegations and denied them as "disinformation laced with slander and innuendo."

(Dissident sources in Moscow also reported that Joseph Begun, 45, a Jewish electronics engineer who has been unable to find work in his field since he applied to emigrate six years ago, was sentenced to two years of exile in a remote area of the country on a charge of vagrancy, news agencies reported.

(In Washington, 24 congressmen signed a letter to Brezhnev protesting "in the strongest possible terms" the plan to charge Scharansky with treason. The letter, drafted by Rep. Sidney R. Yates (D-III.), said "better cooperation between our governments will be fostered" if Scharansky is allowed to emigrate.