American businessmen complained Saturday that new U.S. sanctions against the government controlled by Gen. Manuel Antonio Noriega have thrown them into confusion.

"Don't ask me" how the restrictions will affect U.S. firms, said one manager, speaking on condition of anonymity at a large American company Saturday. "I'm sure it'll take our legal department back home some time to figure it out."The new restraints, announced Friday by President Reagan, forbid payments to the Noriega regime by U.S. citizens and organizations either in the United States or Panama. The executive order also freezes all assets of the Panamanian government in the United States.

Cynthia Farrell, a spokeswoman for the U.S. Embassy, said tax payments should be transferred to the Federal Reserve Bank in New York into an account set up for deposed President Eric Arturo Delvalle, who was forced from office by Noriega in February after trying to fire the general.

The United States still recognizes Delvalle, who has been in hiding, as Panama's legal president.

Noriega, Panama's military chief, has been indicted in the United States on federal drug trafficking charges.

With the United States and domestic opponents trying to oust Noriega, Panama has been thrust into an economic and social crisis. Noriega forced banks to close March 4, and the government has been unable to pay its estimated 130,000 employees and 15,000 troops for more than a month.

A manager of a U.S. franchise in Panama suggested Saturday the president's executive order could give Noriega an excuse to shut down U.S. companies doing business in Panama.

"The U.S. has very little to say in this situation as far as preventing U.S. companies from deciding whether or not to pay taxes in Panama. If you don't pay, your right to operate here can be taken away," he said.

Also looking for answers was Alfredo Arango, spokesman for Petro Terminales, S.A., which operates a pipeline carrying Alaskan crude oil across Panama for shipment to Gulf and East Coast markets in the United States.

Arango said 60 percent of the company's stock is owned by two American companies, Northville Industries Corp. and Chicago Bridge and Iron International, with the rest held by the Panamanian government.

He said the pipeline is the biggest single customer of the state-run electric company, paying it $8.4 million a year.

The U.S. Commerce Department estimated American investment in Panama at more than $4.3 billion at the end of 1986, the last year for which figures are available. It said most was concentrated in petroleum refining, agriculture, fishing, and food processing.

Most U.S. and other foreign firms doing business in Panama are lightly taxed, one reason that many have made the country their branch headquarters for Central and Latin American operations.