The forthcoming trial of leading Soviet dissident Anatoly Scharansky on charges of espionage and treason has now become a dangerous focus for worsening relations between the United States and the Soviet Union, with President Carter's prestige in the Kremlin squarely on the line.

The president's personal word last year that the 30-year-old Jewish computer engineer was never a CIA agent would presumably give pause to the Kremlin. To convict him of that charge, in short, would be tantamount to throwing the lie at Jimmy Carter.

In fact, however, no hint of any Soviet change of heart in the Scharansky case has reached U.S. experts here. That points strongly to an early trial, perhaps starting as soon as next week, following by a punitive sentence. Precisely such treatment was accorded Yuri Orlov, another leading Soviet dissident sent to jail last month for seven years, with an additional five years in exile, on the charge of anti-Soviet agitation - a meager charge compared with treason.

The Kremlin is fully aware that convicting Scharansky will have what one top Soviet expert in the Carter administration calls a "profound impact" on U.S. public opinion. That indisputable judgment, given to us before the president's speech last Wednesday, is now heightened by Carter's words at Annapolis. In a major departure from his recent mild rhetoric on human rights, the president pulled no punches. He condemned "an abuse of human rights in their own country in violation of the agreements reached at Helsinki" that, he said, "has earned them the condemnation of people everywhere who love freedom."

But even more to Carter's point, Soviet President Leonid Brezhnev was bluntly warned that in the United States "public opinion is an integral factor" in the effort to reach agreement on a new strategic arms limitation treaty and that "sharp disputes" with Moscow will unquestionably damage SALT.

The Scharansky case is near the top of the list of "sharp disputes," considering Carter's personal pledge that Scharansky has never been an agent of U.S. espionage.

So the stage is bleakly set for another damaging blow to SALT and further exacerbation of relations between the two superpowers. It is hard to imagine that President Carter, deeply distressed and angered by the Soviet-Cuban moves in Africa, could have bargained for anything less when he addressed the graduating class at the Naval Academy.

That the script is all but written for Scharansky's trial has been taken for granted here for weeks, but even more ominous signals of Soviet intentions are now piling up. Vladimir Slepak, one of the longest-term and most impeccably credentialed Jewish "refusedniks" - Soviet Jews denied emigration visas - was arrested several days ago for hanging a banner from his Moscow apartment with the legend "Let Us Out to Our Son in Israel." He is now in jail on a charge of "malicious hooliganism," and his wife has been notified she will be similarly charged.

Both Slepaks are intimates of Scharansky. Their arrest is presumed to be connected with the Scharansky trial; they would be predictable troublemakers for Soviet "justice" during the course of the trial, reminding the world through the Western press corps in Moscow of the Kremlin's human-rights pledges in the Helsinki agreements.

Likewise, word has seeped into Washington from dwindling remmants of the once flourishing Soviet dissident movement that other Soviet citizens suspected of dissident sympathies are losing the non-resident certificates needed to stay in Moscow. Clearing Moscow of potential troublemakers is standard practice before any major political trial.

Given such persuasive indications that Scharansky's trial is now beyond recall, something in the nature of a miracle would be needed to avoid a new confrontation between Carter and Brezhnev. The record here does not yield a case in which a legal charge against a "dissident" Soviet citizen has been reduced once the trial has started, or for a finding of innocence once the judge has heard the "evidence."

On all these facts, President Carter surely must have been informed. That explains the anxiety now afflicting administration officials emotionally tied to pursuit of detente at almost any price; and the buoyancy fo those who feel the time has come to draw the line.