"It's become obvious now that the American Senate has under-estimated the force of Panamanian nationalism and overestimated Torrijos' capacity to keep that under control," said a diplomatic expert here. "He just hasn't enough political power to have the treaties swallowed here, unless he uses blind force."

This statement reflects not only the outraged reaction here to the American demand to send troops into panama at its own discretion, but also the complexity of Panamanian politics which the American Senate has not sufficiently taken into account. Others suspect that treaty opponents in the Senate - who attached a number of amendments that angered Panamanians - were fully aware of what the reaction here would be.

Brig. Gen. Omar Torrijos's authoritarian government may have virtually unlimited powers on paper, but the military leader actually rules through an informal consensus of interest groups.

For the past 10 years, Torrijos has managed to maintain a delicate balance between a new, demanding left and then politically educated conservatives who ruled Panama in the past. But what ensured his political survival was his able use of the deep-seated emotions of the Panamanians when it comes to the canal.

Through anti-American rhetoric and his promises to make the 70-year-old canal Panamanian, Torrijos has managed to keep some popular support despite discontent here about arbitrary justice, corruption and economic mismanagement.

The Senate's attachment of amendments to the neutrality treaty passed last month, triggered an emotional outcry here that seriously threatens the Torrijos government.

The obvious discontent in Panama has caused concern in Washington as well, Washington Post staff writer Robert Kaiser reported. Well-placed sources in both the Carter administration and the Senate expressed deep concern at the situation in Panama.

Pro-treaty senators have begun discussions about a possible understanding that might be attached to the second treaty still being debated that would state that nothing the Senate has done was meant to contradict America's long-standing recognition of the principle of nonintervention in the affairs of other countries.

Administration officials also were looking for some formula that might reassure the Panamanians without losing crucial votes in the Senate.

Several sources said Sen. Dennis DeConcini (D-Ariz.), whose reservation to the neutrality treaty most angered Panamanians, might hold the key to the outcome of these compromise efforts. The Senate is to vote on a second treaty April 18.

The DeConcini reservation asserts that the United States has the right to send troops into Panama after it takes possession of the canal in the year 2000.

A long-time panama-watcher here said, the Torrijos government's "main success has been pushing the canal issue and being nationalist. If it violates that there is nothing left."

The cost of violating Panama's nationalism became clear last September in the weeks leading up to a plebiscite to approve the two Panama canal pacts.

Bitter about being kept out of the political arena since Torrijos took power in 1968, the formally outlawed opposition parties demonstrated for weeks against the concessions Torrijos had made to the United States in the treaty talks.

The pacts were reportedly approved by two-thirds majority of the voters - although government officials said privately the true majority was somewhat less - but the outcome served as a double warning to Torrijos: not only was there considerable opposition to the treaties, but if Torrijos could not deliver he would be fighting for his political life.

It is believed here that the neutrality pact with its "insulting DeConcini reservation could not pass a new plebiscite, which legal experts say will be required.

Torrijos himselg has always laughed off remarks by American politicians about his being a "tinhorn" dictator or Panama's status as a "banana republic."

But many educated Panamanians now say they have had to swallow too much abuse, citing the American military intervention clause and the language used against them in the American Senate debate.

The Senate debate leading up to the March 16 vote was broadcast live and translated simultaneously on Panamanian radio and television.

"It was incredible to hear those senators talk," a politically moderate lawyer said. "The insolence. They treated us like we were third-rate people. No Latin American would stand for that."

What worries the Torrijos government now is the talk that is heard among usually reserved people like businessmen and lawyers who say they too will take to the streets if the government accepts the treaties with reservations and amendments that some here say are more insulting than the hated 1903 treaty.

Torrijos is acutely aware that he has a politically volatile situation on his hands and has extended the Easter recess of the university and high schools by two weeks to avoid street protests. Some of his close advisers privately concede that acceptance of the pact would mean much more trouble than student disturbances.

Torrijos, who has kept to himself in the countryside during the last 10 days emerged yesterday to make a speech, in which he said, "It is being decided now whether Panama will go on existing as an independent country or not."

"What is at stake may not be this dramatic," remarked a foreign observer here, "but it may well be a question of whether the Torrijos government will continue to exist."