Commerce Secretary Robert A. Mosbacher and nine U.S. corporate chiefs were scheduled to take off yesterday on a trade mission to South America, a region that Bush administration officials believe holds great promise for U.S. exporters.

Mosbacher travels on the heels of U.S. Trade Representative Carla Hills, who returned from the same region last week. Hills was enthusiastic about the "astonishing economic revolutions" that she said are going on throughout the hemisphere as nations turn away from state control toward open markets.

"I'm very enthusiastic about the number of democratic nations saying they are going to turn their back on command economies," said Hills, who attended a meeting in Paraguay of the General Assembly of the Organization of American States as President Bush's special representative.

The idea for the Mosbacher trip resulted from a request by the newly elected president of one of the countries that is in the midst of loosening government controls over its economy.

Brazil's President Fernando Collor de Mello, who is radically restructuring an economy saddled by sky-high inflation and crippling debt, asked the commerce secretary during a January visit here to lead a business delegation to his country.

The Mosbacher group also is going to Chile, whose economy has been the most open in the southern cone of South America but is just emerging from the 17-year military rule of Gen. Augusto Pinochet.

This is the fifth time in less than a year that Mosbacher has acted as the door-opener for U.S. corporate leaders, taking them with him on overseas trips to lend the weight of his office to their sales effort.

These trips are part of a new Bush administration strategy to boost U.S. exports that has included sales pitches on behalf of individual companies by Vice President Dan Quayle during his overseas trips and phone calls by Mosbacher to foreign officials to ensure fair treatment for American bidders for big-ticket contracts.

Although state governors routinely take business executives on overseas selling missions, this kind of activity has been rare for Cabinet-level federal officials.

Foreign trade ministers and heads of states, however, frequently accompany their corporate executives on selling missions.

"In every other country you see heads of governments actively engaged in commercial activities for their companies," said Commerce Undersecretary J. Michael Farren.

"There is a new realization that U.S. firms have interests that have to be considered. If the U.S. government doesn't show an interest ... {in} making sure the game is played fairly, our firms are at a disadvantage," he said.

That new administration policy has drawn some criticism, although it has been applauded by business interests.

Quayle, for instance, was attacked editorially for intervening with Indonesian officials during a visit to that country last year on behalf of efforts by American Telephone and Telegraph Co. to win a $2 billion telecommunications contract. Indonesia put the contract out for new bids after Bush and other administration officials contacted their counterparts in Jakarta in February to counter a Japanese government move to use its political pull to get the contract for NEC Corp., AT&T's rival.

AT&T executives appreciated the help. "The mind shift that seems to be going on in our government is not a bad thing but a recognition of a fact of life" in international business, said AT&T Vice President Randolph C. Lumb.

"We have no opportunity to play in this global business unless we have the government playing a very active role either in making sure that we have a fair opportunity to compete or in many cases helping with the financing," Lumb said.

That same view drew corporate chiefs to the Mosbacher trip. "It is very important {to go with the secretary} because it sends a clear message of the interest both of the U.S. government and the private sector ... to explore opportunities," said Andres Bande, president of Ameritech International and one of the executives on the trip.

"He opens doors and sends a very clear message of U.S. public support for private initiatives," which is particularly important for a company such as Ameritech, which wants to sell telecommunications services to state-owned enterprises, said Bande.

"This is just a great opportunity for me to meet a large number of high officials in a short time," said Marcelo Gumucio, president and chief operating officer of Cray Research Inc., who also is going on the Mosbacher trip.

He said Brazil is a prime market for his company, a world leader in supercomputers.

U.S. exports to Latin America have been growing as the countries emerge from the economic doldrums of the mid-1980s, when their debt crisis appeared insoluble. U.S. sales to Brazil have nearly doubled to $4.8 billion since 1984 while the $1.4 billion in U.S. sales to Chile are up sharply.

In both cases, they are higher than in 1982, when the debt crisis hit and Latin nations were forced to curtail imports.

As an indication of South America's interest in expanded trade with the United States, Paraguayan President Andres Rodriguez asked Bush during a visit to Washington on Friday to restore trade benefits that were taken away during the reign of his predecessor, deposed military dictator Alfred Stroessner.

Rodriguez sought the restoration of the General System of Preferences, which allow Third World nations to ship products to the United States with little if any tariffs.

Commerce Assistant Secretary Susan C. Schwab, director general of the U.S. Foreign Commercial Service, saw the new open-market attitudes in South America when she opened a mining exposition in Chile last month.

She said U.S. companies racked up millions of dollars in sales off the floor, with Caterpillar Inc. selling all of its samples on the exposition's first day. Other South American countries wanted the United States to run similar expositions for them, she reported.