Iraqi President Saddam Hussein invaded Kuwait this week under the pressure of a massive foreign debt that his country is proving unable to pay, as well as discontent within the giant military that is the main pillar of his power, according to Iraqi opposition figures and Western specialists.

While Iraq's debt is massive, there is no certainty as to its size. Analysts have estimated that the hard debt to Western countries is at least $40 billion. Alongside the debt, Saddam is politically obligated to keep money flowing to the military that made sacrifices in his eight-year war with Iran.

Given the secrecy of the Iraqi military establishment and government control of all information in the country, it is unclear how significant or cohesive the opposition is to Saddam from within his military. But unconfirmed reports of senior officers executed or arrested, and of plots against Saddam, suggest that the Iraqi leader does not fully trust his military.

"The major reason {for the invasion} is economic problems," said Saad Jabr, a son of a politically prominent Baghdad family and leader of a London-based opposition group, the New Umma (Nation) Party.

According to estimates by the U.S. government and the London-based International Institute for Strategic Studies, during the middle years of the war with Iran, 1984-86, Iraq spent about 40 percent of its gross domestic product on military expenditures, choking off consumer spending and economic development.

Since the truce two years ago, following eight years of exhausting warfare with Iran, Saddam has sought to rebuild Iraq's economy with oil profits. But the huge debt burden and continued heavy expenditure on the army have stalled the economic recovery he promised his people.

Until this summer, Iraq was working hard to revive its economy by cooperating with its neighbors and the West, rather than confronting them.

Last September, Iraq opened a new terminal in Saudi Arabia to receive its oil, pumped across hundreds of miles of Saudi desert, and load the ships of Iraq's foreign customers. Saudi officials expressed confidence that Saddam, having suffered in his war with Iran, would prove a reliable partner in such economic cooperation. In February, Iraq announced that it would invite foreign companies to return to the country to help develop new oil fields.

But as Iraqi officials spoke optimistically of plans to rebuild their nation with oil and international help, Baghdad was frightening its foreign creditors with repeated failures to keep up payments on its debts. For the past year, financial analysts in the United States and Europe have been saying that Iraq was juggling its debt payments much like any overextended consumer, putting off some bills and constantly running the risk of bouncing its checks.

Last summer, Iraq fell behind in payments to British creditors, traditionally among those whom Iraq had been careful to repay, and British trade officials suspended guarantees for export credits to Iraq.

In September, Baghdad and Paris agreed to reschedule Iraq's debt. France, a major arms supplier, reportedly had not been paid interest by the Iraqis since 1986.

In recent months, Saddam has argued that he should not have to repay about $30 billion he received from his Arab neighbors to prop up his nation during its battle with Iran. The demand that that debt be forgiven was a central element of the confrontation last month within the Organization of Petroleum Exporting Countries that served as a prelude to the invasion.

Saddam is dependent on borrowed cash to keep his political and military machine running and himself in power, according to Iraqi dissidents in exile.

"This large-scale borrowing has become a deliberate policy . . . {so} that the creditors are all locked into the Iraqi debt. It becomes their duty in protecting their investment to support {Saddam's} regime," according to a dissident who monitors the country's finances.

Saddam dismissed the last two governors of his central bank and his previous finance minister for having suggested limits on what the country borrows, the dissident said recently.

Saddam's cash crunch has prevented him from making good on the promise to Iraqis that life would improve after the end of the war with Iran. In part because Saddam has continued to spend huge amounts of money on arms, including development of missile systems and chemical weapons, he has been unable to import consumer goods.

The disappointment of Iraq's postwar hopes has been particularly bitter for the Iraqi military, including officers and their families, according to opposition figures and Western specialists.

"He was never able to provide the things he promised for the families of those killed -- land, grants for houses or cars," said Anthony Cordesman, a Georgetown University professor and Senate staffer who monitors Iraq.

One Iraqi businessman with links to the opposition said recently that officers above the rank of captain had failed to receive promised perquisites following the end of fighting with Iran. However, Cordesman disputed reports that Saddam has had trouble paying his officers. "He has paid the military," Cordesman said. "The problems are because . . . he never gave the officers credit for the victories" in the war with Iran. "It was the Saddam Hussein show."

The New Umma Party's Jabr, one of very few Iraqi exiles to operate openly, said Saddam had four brigadier generals executed in April, accusing them of plotting against him. Jabr said four other generals have been arrested this year. The four, all war heroes, remain in jail, he said.

An Islamic fundamentalist group that seeks Saddam's overthrow "still has its seeds within the military," said Cordesman. He and Iraqi exiles recalled reports that, in January, the group, Dawaa (the Call), tried to assassinate Saddam at an Army Day parade. The reports, in various versions, said a tank in the parade was discovered to be carrying live ammunition, in contravention of rules designed to prevent an assassination.

According to a version offered by one Iraqi exile source, four officers from Dawaa were killed on the spot and the village of the tank unit's commander was said to have been destroyed.