It was the political left that always protested the American presence here but this time it is the people who really run Panama's business who are enraged at the United States.

They are insurance brokers, shipping agents, lawyers and industrialists who speak fluent English and age over 80 banks, hundreds of trading operations, flags of convenience and 50,000 paper companies.

Many got rich or richer as Gen. Omar Torrijos, leading Panama, turned it into one of the world's biggest tax-free laundries of money and goods - an operation more sophisticated than the Canal, and far more important in simple dollar terms.

Torrijos, the populist, calls them the "oligarchs," those middle-and upper-class families who until the 1968 military coup also dominated politics. They put up high-rise offices along the boulevards of Panama City and rambling homes at the golf club and the oceanside. Without them, many say, Panama would be largely banana plantations and a canal.

Torrijos never liked the pro-American business community, although he wooed them to keep the economy going and they, at times, have twisted his arm by halting investments and sending their money to the United States.

But now Panama's "oligarchs" are emotional and indignant about the U.S. Senate's demand that the United States be free too send troops into Panama as it sees fit. Reacting to the reservation sponsored by Sen. Dennis DeConcini (D-Ariz.) and accepted by the Senate, they say things like "over my dead body" or "I'd be willing to change my clothes and fight."

It was the protest of the powerful business community, more than of the leftist intellectuals or legal experts, that has convinced the government that a treaty containing a broad American intervention right will not be swallowed in Panama.

One of these businessmen, widely respected among his colleagues, is Joaquin Vallarino, whose family owns one of Panama's largest breweries and the Coca-Cola concession, with more than 400 employes.

Vallarino is soft-spoken, affable, educated at Dartmouth. He thinks it would be hard to find three countries in the world more pro-American than Panama.

"But when I saw the first reservation saying American troops could land here when they wanted, I was so mad, I didn't even read the rest. It can lead to bitter and dangerous things I'd rather nor speculate about."

Vallarino was pacing his office on the second floor of his Del Baru beer brewery. Although he has headed several businessmen's organizations he never involved himself much in politics. Vallarino said he voted a whoehearted "yes" in Panama's plebiscite on the treaties "because a treaty was badly needed."

"But why did they have to keep digging about how, when and where the troops would come and rape us?" he asked angrily.

"All right, we had to consummate this act with the Americans, but then we had to let ourselves be crucified, too. It's too bad it couldn't happen without one insulting the other. Regardless of what happens now there are a lot of unnecessary wounds and scars."

The dilemma now for Panama's businessmen is how far to support Torrijos between an economic crisis and an unacceptable American demand. Holding back their support would mean a further slump in Panama's ailing economy and their voice is therefore crucial. They have long wanted to get rid of the military regime, which gives them little voice in the decision-making process, has persecuted some and has frightened others with social change.

Yet if it comes to choosing between the Torrijos government and signing an American intervention clause, they insist, they are on Torrijos' side.

Last week the broad-based National Council of Panamanian Business Associations announced it rejected not only the "insulting" intervention clause but also the amendment introduced by Sen. Sam Nunn (D-Ga.), which spells out how Panama is to use any Canal revenues.