An Iraqi firing squad has executed 21 men, including five top officials, after they were convicted of conspiring against the new government of President Saddam Hussein, the Iraqi news agency reported yesterday.

The executions in oil-rich Iraq reflect increasing turmoil in the leading rejectionist Arab nation that could affect the overall Middle East situation.

Although speculation continued that a foreign power was involved in the alleged conspiracy, informed sources in Washington believe that the action more likely represents an attempt by Saddam Hussein to consolidate power.

The death sentences were carried out by members of "civilian and military organizations of the [ruling Baath Socialist] Party from different parts of the country using their own weapons," the official government news agency said. Saddam Hussein witnessed the executions, it said.

Among those executed were five former members of the Iraqi Revolutionary Command Council, which Saddam Hussein heads. They included Deputy Prime Minister Adnan Hussein, who served as the council's secretary, and Education Minister Mohammed Mahjoub Mahdi.

The special Iraqi court sentenced a 22nd man to death, but the news agency reported that he was "nowhere to be found." Thirty-three persons were given prison sentences ranging from one to 15 years. Thirteen others were acquitted.

Charges of a conspiracy were announced July 26, just 10 days after Saddam Hussein came to power when President Ahmed Hassan Bakr resigned.

At the time, Iraqi press reports claimed that an unidentified foreign power was masterminding the alleged conspiracy in an effort to undermine the government's opposition to the Egyptian-Israeli peace treaty.

Other reports suggested that Saddam Hussein believed Syria was involved in the alleged plot and that the Iraqi government did not want to hurt the anti-Israeli cause by making the accusation publicly.

There also was speculation that the alleged plot may have resulted from Saddam Hussein's weakening of ties with the Soviet Union and movement toward better relations with Western Europe.

Others pointed to rivalries between the Shiite Moslems Sunni Moslem sects. While Shiites form a slight majority of Iraq's population, most of the country's military and political leaders are Sunnis.

Speculation that the trials were motivated by religious rivalries was fueled by a government crackdown on Shiite Moslems who protested the arrest of Deputy Prime Minister Adnan Hussein. He was a Shitte.

Western analysts are watching closely for any signs of serious religious strife in Iraq because of the impact this could have on other oil-producing countries in the Persian Gulf. Saudi Arabia has a 10-percent Shiite minority, which is located in that country's oil-producing region. The Islamic revolution in Iran was led by Shiite holy men under Ayatollah Ruhollah Khomeini.

Informed sources noted, however, the seven-member court that handed down the death sentences contained three Shiite members. The membership was seen as an effort to preclude the interpretation that the trials were religiously motivated.

Speculation that Syria might have been involved in a plot against Iraq also were unlikely, one U.S. government source said, because the government of President Hafez Assad was "at pains to avoid strife. The hatchet has been officially buried, and Syria has enormous problems of its own."

Also, although Syria and Iraq had been bitter rivals, they have grown increasingly closer in an alliance against Egypt's peace efforts with Israel. Assad reportedly gave Iraq personal assurances that his government was not involved in any conspiracy.

While Moscow may be upset by the cooling of relations with longtime ally Iraq, sources point out that the Iraq Communist Party is so fragmented and weak as to preclude any major move against the government.

U.S. sources said there was no indication of any Libyan or Egyptian interference in Iraq.

One U.S. source speculated that the best explanation might stem from the fact that the executions followed "a takeover of power by a civilian who succeeded a military leader" and was attempting to cut off opposition.

An Iraqi diplomat also downplayed theories of foreign intervention. "It was merely an attempt by a greedy clique to seize power," he said.

While large numbers of Iraqis still await trial, the executions may not continue if Saddam Hussein mainly wanted to demonstrate his strength to opponents, one source said.

U.S. government sources said they do not expect the Iraqi turmoil to affect Iraq's 3.5 million barrels-a-day crude oil production. Iraq's increasingly important diplomatic activity and its expanded arms purchases make the oil revenues a necessity, they said.

Iraq principally exports its oil to Europe, they said. The United States does not deal directly with Iraq for oil, but would be affected by any major shifts in world supplies.