Two investigative reports in the U.S. media this month contend that there is substantial circumstantial evidence that links Soviet Bloc intelligence agencies to the Turkish gunman who shot and seriously wounded Pope John Paul II in May 1981.

American officials who have followed this situation say that the U.S. intelligence community assessment agrees there is circumstantial evidence for strong suspicion that the Soviet security agency -- the KGB -- either knew about the plot against the pope or promoted it. But, these sources say, there is no "smoking gun" that proves a Soviet role.

The public reports, one in the current edition of Reader's Digest and another produced by NBC Television and scheduled to be broadcast Tuesday, suggest that the Kremlin either plotted or acquiesced in the attempted murder of the pope because of Soviet dissatisfaction with the pontiff's strong support for the now-suspended independent union Solidarity in his Polish homeland. A preview of the NBC report, by correspondent Marvin Kalb, was shown to reporters yesterday.

Radio Moscow, reacting to the already published Reader's Digest article by Claire Sterling, has denounced such allegations, calling them "absurd" and "unfounded."

A central argument of both reports is that the 24-year-old gunman, Mehmet Ali Agca, obtained his forged passport and the Browning 9-mm automatic used in the attack from associates of a shadowy Turk named Abuzer Ugurlu, who worked mostly out of Bulgaria and is said to have links to Bulgaria's secret service. NBC reports Italian investigators as saying that an Ugurlu associate sent a courier to Agca offering him 3 million West German marks and sanctuary in Bulgaria to shoot the pope.

U.S. officials say Agca got both his passport and his gun in Sofia, the Bulgarian capital, in 1980.

Agca, 24, is serving a life sentence in Italy for shooting the pope on May 13, 1981. He admitted at his trial that he had shot the pontiff but did not identify who financed his travels through several European countries before he reached Italy.

While the public reports do not directly implicate the Soviet KGB in the shooting, they contend that Bulgaria is one of the Soviets' most obedient allies, that the Kremlin knows everything that is going on in Bulgaria on security matters, and that Bulgarian intelligence would be unlikely to act without Soviet approval.

The American intelligence assessment also is based heavily on the Bulgarian connection, sources say, in combination with analysis of Agca's movements around Europe, money that was paid to him, and the timing of the attack upon the pope, which came as the Solidarity movement was gaining strength. "If there was no Solidarity movement, then I suppose everyone would believe Agca was just a kook," one source said.

Sources said, however, that the assessment officially does not go beyond casting strong suspicions on the Bulgarian secret service, although it is widely assumed in the intelligence community that the KGB was behind the Bulgarians. Sources say former secretary of state Alexander M. Haig Jr., who has had some disputes with the intelligence community before about the extent of Soviet involvement in terrorism, is the one who seems most convinced of Moscow's role.

There also are some intelligence analysts who are said to be dubious about a Soviet link, believing that the KGB would not have chosen a plan in which the assassin was virtually certain to be caught.

Some officials here believe that money may be a big factor in explaining the possible conspiracy. Bulgaria is said to be a major center of the international gun-running trade and sources say the Bulgarians have gotten lots of business by supplying both sides in the civil strife in Turkey. Some officials believe that the Bulgarian sercret service may have promised Ugurlu, the alleged kingpin of the smuggling business, a better deal if he could use his contacts with the Turkish terrorist groups to recruit an assassin. Ugurlu reportedly is under arrest in Turkey, although it could not be immediately determined here if charges against him have any connection with the assassination attempt.

The Digest article suggests that Agca may not have known who his true backers were. Author Sterling also has written a book, "The Terror Network," which suggested that the KGB was a major promoter of international terrorism.

Before Agca shot the pontiff, Turkish police had identified him as a member of a neo-fascist Turkish terrorist group called the Gray Wolves. Both NBC and Reader's Digest suggest that Soviet Bloc intelligence services may have chosen Agca as a hired gun because he was known as a rightist and thus would not be suspected of links to the East.

Italian officials who prosecuted Agca have said that there were signs that Agca had received assistance from other persons. The NBC report also quotes a Vatican official, Cardinal Silvio Oddi, as saying that "we suspect, we think" that a foreign power may have been behind the shooting, possibly because of "international political strategy." NBC also quotes unidentified papal aides as saying that John Paul believes the Russians were behind Agca's attempt to kill him "and that they might try it again."