Five persons were executed early this morning for their role in the latest of a wave of alleged plots against the government, Tehran radio reported.

Closed trials began yesterday for 300 suspects, and Ayatollah Ruhollah Khomeini called for execution of "all of them without any exceptions."

Those executed at 1 a.m. today included Ahmed Mohagheghi, a retired Air Force general and former chief of the gendarmerie who allegedly was one of the ringleaders of the plot.

The secret revolutionary tribunals at Evin Prison reportedly were to continue throughout the day.

The government earlier said the trials would be open and that documentary evidence of alleged involvement by the United States, Israel and Iraq would be presented.

Khomeini, in a speech to the Revolutionary Guard, left little doubt that there would be executions of the alleged plotters, most of them military personnel.

"Those who were, in this corrupt way, thinking of a coup d'etat, all of them without any exceptions, should receive the verdict of death according to the Koran," he said, adding that the Koran, the holy book of Islamic law, provides four ways of dealing with such people, "the least of which is that they should be killed." He did not list the other possible penalties. i

In a country where in the last 18 months about a thousand persons have been executed, many for such lesser crimes as prostitution and selling drugs, Khomeini's remarks were taken as an indication of a harsh crackdown on the alleged plotters.

Despite the harshness of the sentences likely to be meted out, some officials are trying to play down the most recent coup attempt and some question whether it actually happened.

Iran in the past week has gone through all the traditional activity that follows the announcement of a failed coup: scare headlines, a police dragnet leading to hundreds of arrests, a purge of the military and closing of borders.

Yet few informed persons outside the government hierarchy believe that a major attempt was made to overthrow the regime with foreign involvement as Iran has claimed.

Many sources agree that the government probably discovered, at most, a plot in its infancy, and far from ready for the kind of technical coordination required to seize an airbase and bomb key government installations, including Khomeini's home, as reportedly had been planned.

Still, the outburst of emotion might have been understandable if this had been the first time Iran's Islamic revolution had been endangered since ousting shah Mohammad Reza Pahlavi.

By President Abol Hassan Bani-Sadr's own count, however, this was the sixth unsuccessful takeover attempt since he took office in January, and he said the government already had information about a seventh.

Some diplomats believe that this time opposing elements in Iran's byzantine politics seized on the latest plot to enhance their own causes.

According to this theory, Bani-Sadr wanted to use the alleged coup to unify the country behind him as he is about to select a parliamentary government to try to bring order out of 18 months of revolutionary chaos.

Instead, his opponents in the hard-line clerical Islamic Republican Party appear to have gained the advantage. They have used the coup to purge the military and in some areas have brought it under the control of the Revolutionary Guards, who are often outside the president's authority.

Information about the military is closely guarded, but one source said even though there might be officers still around who were willing to launch a coup, support would not come from within the ranks.

The Iranian public, however, provides a fertile ground for conspiracy theories, especially involving foreign nations. With the country having held 52 American hostages for nine months, there is widespread concern that the United States will seek to undermine or overthrow the government.

Nonetheless, some Iranian officials are saying that the most recent plot's scope has been exaggerated.

Brig. Gen. Ali Zahir-Nezhad, commander-in-chief of Iran's ground forces, told Pars, "The issue has been made to look far too big. . . . This coup d'etat was not the main plan. It may have been a step toward a larger conspiracy."

Foreign Minister Sadegh Ghotbzadeh said: "It was not really that important. I think everybody exaggerates it."