A group of U.S. corporations, lured by the potential for capitalist profits in an officially Marxist nation, are starting to take advantage of a controversial Reagan administration foreign policy designed to bolster the leftist government of Mozambique.

Amid a growing political debate fueled by New Right activists, a handful of companies such as Tenneco Inc., Teledyne Corp. and other American multinationals recently sent representatives on a U.S. government-sponsored trade mission to Mozambique, headed by former Defense secretary Melvin Laird.

The idea, endorsed by the Reagan administration, was to spur U.S. corporate reinvestment in that mineral-rich and strategically located southern African nation for the first time since 1975, when the country's Portuguese colonizers were overthrown and a new pro-Soviet government headed by Samora Machel took power.

But some conservatives, who have been bitterly critical of administration policy toward southern Africa, see a fundamental contradiction in promoting such trade; Mozambique, they argue, is no different from Nicaragua in that both nations are headed by Marxist regimes fighting pro-Western guerilla insurgencies.

Yet in Nicaragua, President Reagan has imposed a trade embargo barring U.S. companies from doing any business with that country. In Mozambique, the administration has taken precisely the opposite tack: offering economic and even military aid to the Machel regime and encouraging American companies to invest.

For conservatives, the incongruities don't stop there. Liberal activist groups have made a major issue of pushing for U.S. corporate disinvestment from neighboring South Africa, charging that the presence of American companies lends legitimacy to a racist regime guilty of gross human rights violations. Yet in Mozambique, a country with its own East German-trained secret police force and thousands of political prisoners, American companies are being openly encouraged to invest with no protests from U.S. citizens, they say.

"This is particularly shameful for this administration given its rhetoric on behalf of freedom fighters," said Howard Phillips, chairman of the Conservative Caucus, who has founded a group called the American Committee to Rescue Africa From the Grip of Soviet Tyranny.

"They're clearly trying to develop a vested interest on the part of American banks and business in propping up the regime in Mozambique," he added. "It shows the basic split in the Republican Party between those who support freedom and those who are guided by the profit motive."

For their part, State Department officials make no bones about the fact that they want to see U.S. companies return to Mozambique.

James Libera of the State Department's Bureau of African Affairs said, "It is indeed our policy to encourage trade and investment in Mozambique. It's part of our new policy. . . . We think this can contribute to showing Mozambique the benefits of the private sector."

As administration officials see it, this approach to an avowedly leftist government is justified by international geopolitics and internal changes within the regime itself. While still clinging to his Marxist rhetoric, Machel has shown his growing disenchantment with his Soviet sponsors and made overtures to the West.

Over the past year, as its destitute economy has all but collapsed, Mozambique has signed a nonaggression pact with South Africa, joined the World Bank, submitted its books to the International Monetary Fund and exchanged ambassadors with the United States.

Even though Soviet and East German advisers remain in the country, administration officials argue that U.S. aid -- backed by U.S. corporate investment -- gradually will wean Mozambique away from the Soviet Bloc, producing a major diplomatic coup for the West.

While the political wisdom of this policy is still being debated on Capitol Hill -- an administration request to provide $1.1 million in counterinsurgency trading to the Mozambique military has been stalled in a Senate subcommittee -- there is little doubt that U.S. rapprochement is beginning to bear fruit for U.S. companies.

David Rockefeller, retired chairman of Chase Manhatten Bank, has made two trips to the country in the past year, while Lehman Brothers, the New York-based investment banking firm, has signed a contract to serve as financial advisers to the Machel government. In addition, four major oil companies -- including Arco and, as part of a joint venture, Exxon and Shell -- have signed agreements to spend up to $400 million to develop Mozambican oil over the next five years.

With the potential for additional huge mineral finds, other large U.S. companies are considering plans to reinvest in the country, according to Henry Thomas, president of Trade Management International Ltd., which coordinated the recent trade mission.

Laird is an investor and until recently was a director of Trade Management, which, according to Thomas, hopes to serve as a broker between U.S. companies and Mozambique. The former defense secretary did not return several phone calls to his office.

"There was no presence of American corporations at all for about 10 years," Thomas said. "The door was slammed shut. But within a year's time now, that door has been thrown virtually wide open."

One sign of that was the trade mission, which included representatives from Signal Companies Inc., Caltex, Teledyne Corp., Science Applications Inc. and Tenneco, the huge Houston-based energy conglomerate, which sent three representatives on the trade mission.

Jack Ray, Tenneco's senior vice president for international development, said the firm wants to sell construction equipment for a large-scale irrigation project being planned by the government and foresees a potential market of about $2 million to $3 million in sales annually.

Tenneco's Cace subsidiary was a major supplier of equipment to Mozambique when it was still a Portuguese colony. But when company officials returned during the recent trade mission, "We found a lot of our equipment was there but not usable because they've had no spare parts for 10 years. . . . The country was in a state of disrepair, the infrastructure -- the roads, the port -- had fallen apart."

Asked about criticism from conservatives that American companies such as Tenneco were playing into the hands of a Marxist regime, Ray replied, "All I know is, we're trying to sell equipment. We're not trying to prop up the government. If we don't sell equipment, someone else will."