Even in these cynical times, when Americans have been conditioned to believe the worst, the sensational charges and countercharges surrounding the "Libyan hitmen squad" reports are setting a new standard of incredibility.

Not that there are no assassins. There may well be. We in the press are hardly capable of proving or disproving the case, and a generation of exposure to the reality of assassination attempts, successful or not, removes much disbelief.

But what makes these death-threat stories even more extraordinary--and raises serious questions about them--is the public nature of the accusations.

Here is the president of the United States, chatting with reporters yesterday and directly accusing the leader of a foreign state of plotting to kill him and other American leaders. "We have the evidence, and he knows it," the president said, referring to Libya's Muammar Qaddafi.

This comes after days in which the U.S. government has been building a concerted case, through statements and leaks to the press, of the gravest sort of charges against Qaddafi and his regime.

Our television screens and front pages have been filled with fearsome accounts of terrorists infiltrating our borders, of FBI agents fanning out to capture them, of SWAT teams guarding the roof of the White House, and film footage of Libyan soldiers using Soviet missile launchers to shoot down helicopters such as the one the president rides in.

In other times, such statements would mean we were on the brink of war. Now, the war that is being waged is one of headlines and TV interviews.

Qaddafi denies that he plots to kill Reagan. It is we who are plotting to kill him, he says (just as, a generation ago, we tried to remove another thorn in our side, Fidel Castro). The president disagrees. He is out to kill me. And we watch it all, live and in color, courtesy of the equipment of the electronic/space-satellite age.

In other times, too, this strange episode would have brought an instant surge of public anger and a rallying of support for the president. That does not seem to have occurred.

For now, and absent more of the president's evidence, the public appears to have adopted a wait-and-see attitude.

In the meantime, the government continues to give the highest official blessings to the widest circulation of the most sensational stories to reach the public in years. It's almost as if public opinion were being prepared for dramatic action--say a strike against Libya or Qaddafi himself.

The record of recent months has made either prospect more than idle press speculation. Throughout this year, the U.S. rhetoric about the threats emanating from Qaddafi's Libya has been increasing in volume and severity. It is reminiscent of the talk about Castro in the days when the United States was planning the Bay of Pigs invasion, and, in fact, commissioning assassination schemes against Castro.

Even a cursory examination of newspaper files shows an ever-hardening official line against the leader of what only a few years ago was the poorest of Arab states.

For instance:

At the time of Ronald Reagan's inauguration, official U.S. estimates prepared for the new administration pointed to increasing problems with Libya. References were made to "Qaddafi's longstanding sense of Pan-Arab and Pan-Islamic revolutionary mission which has led him to intervene in about 45 countries in the Middle East, Africa, Europe, Asia and Latin America."

Reports were made of Qaddafi training "suicide squads" for commando-type actions.

By spring, the papers were reporting official concern about the growing threat of Qaddafi to stability in the Mideast. A Washington Post article in March, for example, began this way:

"While the new U.S. administration studies defense budgets and Caribbean military scenarios, the Soviet Union has been effectively building a potential military threat to southern Europe and to U.S. Mediterranean sea and air communication in Libya. More than 5,000 eastern bloc military and civilian personnel, including Cubans, and an immense $12 billion arsenal of mainly Soviet weapons are in Libya, according to senior U.S. and allied intelligence sources."

Adding to these kinds of stories were reports last spring about former CIA and Green Beret personnel training assassination teams inside Libya.

Summer brought the U.S. 6th Fleet maneuvers off Libyan shores, and renewed tension. After American jets shot down two Libyan planes over the Gulf of Sidra--which Libya claims as within its territorial waters--Qaddafi publicly accused the United States of having a "premeditated plan to launch military aggression against Libya and to invade it."

Libya was prepared to defend its territory even if it meant a third world war, he said.

Fall brought even harsher language. Sudan, Libya's neighbor to the south, was reporting stepped-up military action against it from Libyan-backed forces.

The struggle inside Sudan was an old one, with big power stakes. Sudan has been backed by the United States in its dispute with another neighbor, Chad. Libya, with Soviet support, has been assisting the Chad guerrilla forces fighting inside Sudan.

That situation became more serious in the days just before Egypt's Anwar Sadat was assassinated. The weekend before he was murdered, Sadat dispatched his vice president, Hosni Mubarak, to Washington bearing what U.S. reporters were told was a "very urgent message" for Reagan. The mission was to alert Reagan to the growing likelihood of military action along the Sudanese border with Chad. Mubarak asked for the U.S. government to send additional arms, including antiaircraft missiles, to Sudan.

After Sadat was slain, the language about Qaddafi became even more vitriolic. On the flight back from Cairo aboard the president's plane, former presidents Jimmy Carter and Gerald R. Ford made extraordinary comments about Qaddafi.

Carter characterized him as in some ways "sub-human." Ford called him "a cancer" on that part of the globe, and spoke openly of U.S. action against him.

Now, in the latest and deadliest part of this true-life story of murder plots and terrorist teams, the American president speaks publicly about plans for Libya to topple the top U.S. leadership.

At this writing, much about this episode remains unfathomable. There are more questions than answers. But a historical irony also exists.

For generations, American romantic lore has been fueled by stories of heroic military action. "To the shores of Tripoli" remains a symbol of a daring American mission.

Now, so much later, we are told to beware of a reverse deadly mission, from the shores of Tripoli.