Jewish activists said today that Anatoly Scharansky and 11 other prominent political prisoners soon will be freed as part of a move by the Soviet Union to improve treatment of Jews trying to emigrate.

The Soviet actions, if carried out, would represent significant concessions to the United States and Western countries near the eve of next month's summit conference in Vienna between President Carter and Soviet leader Leonid Brezhnev.

The report, which has not been confirmed by the Soviet government, came from dissident figures here who said it grew out of a meeting Friday between a high-ranking Soviet official and Robert Hawke, president of Australia's council of trade unions and a major figure in Australian politics.

Hawke left Moscow today without talking to reporters. In Rome tonight, he said that "good news" was ahead, United Press International reported, but he said he would say no more "for fear of blocking future developments."

An associate of Hawke, reached at Hawke's hotel in Rome, said there were still some "loose ends" to be tied up before Hawke discussed the matter publicly, but he said accounts of the Soviet offer made public by the dissidents in Moscow are accurate.

It was not clear, however, what the Soviets actually said about the fate of Scharansky and the others, an issue that could prove pivotal in the Carter administration's effort to gain ratification in the Senate of the new strategic arms limitation agreement that Carter and Brezhnev are to sign in Vienna.

The names of Scharansky or other individuals were not mentioned in Hawke's talks with the Soviets, according to sources, but it was "clear who was involved."

Moscow activists, led by Alexander Lerner, a Jew who has long been refused permission to emigrate, said Hawke told them Friday night that he had met with Alexei Shibaev, a member of the Communist Party Central Committee and chairman of the powerful State Trade Union Council.

According to Lerner, Hawke said that the Soviet official promised that the Soviet Union soon will:

Release 12 Soviets who have been imprisoned or exiled for Jewish activism. The list of 12 names that had been submitted to Soviet officials includes Scharansky and Vladimir Slepak, another prominent dissident. Also on the list are the last three jailed members of a 1970 Jewish air hijacking plot. Seven others were released by the Kremlin last month.

Issue exit visas to Jews who have been denied emigration on state security grounds for more than five years. Lerner estimated that about 200 persons are in this category, including himself and his wife.

Establish a firm limit of no longer than five years for denial of exit visas on security grounds.

Lerner and Hawke discussed the Moscow Jews' demands Wednesday for two hours. The dissidents' position included the three points the Soviets are said to have promised to fulfill, plus a Jewish demand for less red tape for visa applicants, which the Soviets ultimately refused to consider. In return, Hawke was told he could offer the Soviets a statement by Lerner and the others that conditions had markedly improved for Jews here.

The four-hour session Friday between Shibaev and Hawke and his wife is a bizarre example of recent Moscow maneuverings to improve its image. The Kremlin has cast Lerner and other longtime Jewish activists in the role of subversive Zionists aiming at undermining the state on behalf of hated Israel and imperial America.

That a senior government official would bargain with a go-between for such outcasts indicates the lengths to which the Soviets may be trying to go to extricate themselves from their Western public relations disaster. That they would promise to take such steps in return for a public statement of praise also hints at Soviet eagerness to bring an end to the U.S. trade restrictions imposed by the Jackson-Vanik amendment to the 1974 trade act, which ties improved trade credits for the Soviets to eased Jewish emigration.

Shibaev shuttled between bargaining table and telephone, giving Hawke the clear impression that the Soviet, an 18-year Central Committee member, was relaying the substance of the talks and getting instructions from "much higher circles," according to Lerner.

Shibaev did not give specific individual promises by name on the release of Scharansky or any of the other 11, Lerner said. Hawke apparently talked only in general terms of the "12 Jewish prisoners of conscience," but Lerner said today that could only apply to Scharansky and the others.

Lerner said Mrs. Hawke from shorthand notes later quoted Shibaev as saying, "Please tell these people [the Moscow Jewish leaders] that Soviet authorities have decided to release the prisoners, and the refusedniks and set a five-year refusal limit."

When the Soviets accepted the three Jewish demands, they then asked for a positive statement from Lerner and the others.

"I gave them such a statement," said Lerner. Its wording was worked out Friday night and Hawke delivered it to Shibaev at 7 a.m. today.

Cautiously worded, the statement signed by Lerner Viktor Brailovsky and Vladimir Prestin, describes the three Soviet promises and asserts, "We consider that the fulfillment of these intentions means a profound improvement of the emigration policy and it should be responded to positively by the world."

So far, the Soviets have taken no known steps that reflect their promises to Hawke. Lerner said he and his friends have set an informal one-month deadline for some sign of good faith by the authorities.

From the beginning, I didn't believe it," he said today. "But now it doesn't look like a trap, not a trick. Is it a joke? This is too dangerous for jokes."

Western diplomats greeted the account with hardened skepticism and surprise at what many consider the unlikely choice of Hawke as a conduit for such a move, since he is not widely known outside Australia.

At the same time they point out that good will gestures can be expected on the eve of important international summit meetings. Brezhnev last month abruptly cut short the prison terms of five of the Leningrad hijackers, and later, the Soviets and the United States achieved the unusual exchange of Alexander Ginzburg and four other dissidents for two convicted Soviet spies.

In addition, the Soviets have significantly raised Jewish emigration this year, allowing a record 5,000 to leave in April alone, and perhaps as many as 50,000 for the year, another record.

Hawke, who is known to be eyeing a try for national political office in Australia, has concerned himself deeply with Jewish affairs for some years. He is said to have a personal friendship with Israeli Prime Minister Menachim Begin and came to Moscow from Israel for this visit.

Seen from here, the Soviet choice of such a man to play a role in what would be a major Kremlin gesture could be part of a complex process of unlikely moves by the Brezhnev leadership to skirt a direct confrontation with Carter over Scharansky - whom the the president has personally defended - and bolster the Soviet image just before the summit. CAPTION: Picture, Anatoly Scharansky recently was reported weaving potato sacks in a Soviet prison. Union of Councils for Soviet Jews