They flashed the first news of the Argentine capture of the Falkland Islands in 1982, described the havoc caused by last year's earthquake in Mexico and kept up a running commentary on the Soviet invasion of Czechslovakia. This past week, they have provided the world with a vivid first-hand description of the disaster at the Chernobyl nuclear power plant in the Ukraine.

In an age when wars and revolutions are routinely broadcast by satellite into America's living rooms, the lone ham radio operator is like a mythical figure from the past, defying breakdowns in regular communications. In the case of the Chernobyl catastrophe, however, the authenticity of the crackling voices on the shortwave band has been hotly disputed.

On one side of the dispute are radio enthusiasts in the Netherlands and Israel who claim to have heard Ukrainian hams in the vicinity of Chernobyl describing a panicky scene after the explosion at the nuclear reactor. On the other, are numerous radio hams scattered all over the world who doubt the existence of their Chernobyl colleagues, partly because they have never been able to catch them and partly because their outspokenness seems so out of character with the caution usually displayed by Soviet hams. Frustrated by the Soviet information clampdown, news media here and in the United States gave a good deal of attention Wednesday to a claim by Dutch radio enthusiast Annis Kofman that he had heard a Ukrainian ham talk about "hundreds of dead and wounded." According to Kofman, the Soviet ham spoke of tens of thousands of panic-stricken people moving south with their cattle and children.

An even more spectacular claim was made by an Israeli amateur radio operator, David Ben-Bassat, who said today that he has had four separate conversations with a Soviet ham living near the devastated nuclear plant. Ben-Bassat has supplied tapes of the exchanges, in which a heavily accented Russian voice said he wanted to tell the world what was going on, to NBC News which has used them on television and radio.

In theory at least, both claims are plausible. There are an estimated 75,000 amateur radio operators in the Soviet Union, including many in the Ukraine. Soviet hams are well-organized, frequently heard on the shortwave band and attend international conferences.

In practice, however, Soviet hams are tightly controlled by the authorities, according to their counterparts in the West. Licenses are given only to loyal Communist Party members. The KGB, the Soviet secret police, is known to monitor the most widely used shortwave bands. Conversations with Israeli hams have been strictly forbidden since the 1967 Six-Day War when Moscow broke off diplomatic relations with Tel Aviv.

"A Soviet amateur could lose his license for talking with an Israeli," said Ahron Kirschner, president of the Israeli Amateur Radio Club, in a telephone interview. Kirschner said he was "skeptical" of Ben-Bassat's claims to have spoken with a Ukrainian ham for reasons he was reluctant to divulge.

Another club official, who asked not to be named, said: "I don't think that Ben-Bassat is lying or hallucinating, but I do think he could easily have been cheated. There are people who go on the air, pass a message and then hold their stomach laughing at everyone's gullibility."

Ben-Bassat, who has been monitoring radio transmissions for 27 years, said he was convinced of the authenticity of the Ukrainian ham "He could easily have been cheated. There are people who go on the air, pass a message and then hold their stomach laughing at everyone's gullibility." -- Israeli radio club official who gave a call sign that identified him as from the village of Chernovych, about 30 miles from Chernobyl. He said he had heard the Ukrainian ham speaking Russian to a Soviet colleague.

A recording of two of the conversations conducted by Ben-Basset was made by an NBC television crew, proof that he was at least talking to somebody, even if it was not a ham just down the road from Chernobyl, as he maintains. In his most recent message today, coming in at force seven on 14.110 mhz, the Ukrainian-sounding voice spoke of about "700 casualties including 60 dead."

"We have no reason to doubt the authenticity of these conversations but there some things you have to accept on faith," said Bert Medley, an NBC producer in Tel Aviv. He described Israel, which is 1,200 miles from Chernobyl, as an excellent "monitoring post" for events throughout Europe and the Middle East.

Support for Ben-Bassat also came from Micky Gurdus, the doyen of the Middle East radio monitors with a string of scoops to his credit. Gurdus, who also works for NBC, said that he was initially suspicious about the existence of the Chernobyl ham but changed his mind after listening to the tapes. He said the broadcasts appeared to be coming from the general direction of the Soviet Union.

Both Ben-Bassat and Gurdus said they thought the Chernobyl ham was probably Jewish, a possible explanation of why he was willing to risk talking to someone in Israel.

Radio hams elsewhere in the world, however, remained suspicious of the reports. Karl Muller, a senior staff adviser at the American Radio Relay League, said he was "surprised" by the reported conversations. He said that American hams who have succeeded in raising the Soviet Union since the accident have received reassurances that everything is fine in the Ukraine.

The credibility of the Dutch radio enthusiast, Kofman, has been challenged by the Radio Society of Great Britain. A club official, Jack Nelson, said he found it "striking" that no other ham had reported hearing the same conversation even though it purportedly took place on a heavily used frequency, 14.187 mhz.

"When the Argentinians invaded the Falklands, we got 20 or 30 calls of the same conversation," said Nelson who noted that there were about 2 million active radio hams, including 25,000 in Britain alone, all glued to much the same frequency as Kofman. He added that he had never heard of any dissident-sounding broadcast by a Soviet ham.

Defending his scoop, Kofman said the Soviet ham had talked on Tuesday night about explosions occurring at two of the Chernobyl reactors, not just one. This news was later apparently confirmed by satellite pictures the following day, but it has since been questioned by U.S. intelligence sources.

Asked why he did not make a tape of the broadcast, in which the Soviet ham was allegedly talking to a colleague in Japan, Kofman said: "I didn't have a tape recorder handy. But perhaps it was just as well. A recording could have helped the Soviet authorities track him down and arrest him. After all, he broke all the regulations."