The U.S. Chamber of Commerce, one of the main business voices in the country, has formally broken with hard-liners in the Reagan administration over their effort to delay or block construction of the multibillion-dollar Soviet natural gas pipeline to Europe.

In a letter sent to President Reagan on Feb. 5 and made public yesterday, chamber President Richard L. Lesher warned that the administration appeared to be on the brink of a "profound change in policy that could be likened to a strategy of economic warfare" against the Soviets.

Lesher, whose organization is a mainstay of support for the administration on most issues, noted that a policy of denying hard currency to the Russians by hampering their energy exports would raise a "new and unprecedented issue which goes to the core of U.S. policy on East-West trade" and he urged Reagan to consult the business community before adopting such a stance.

However, even as the chamber was rallying in support of East-West trade, Reagan administration officials yesterday were considering asking the western allies to go along with a new kind of economic sanction against the Soviets.

Under a plan circulated in the administration, West European governments would agree to cut off all new credits and loan guarantees to the Soviets--a step that probably would force Moscow to pay cash for any new western technology and equipment, since private banks presumably would be reluctant to extend credit without government backing.

Officials supporting this option say it has several virtues.

It would allow the West Europeans to go on selling nonstrategic equipment and technology to the Soviet Union. Up to now, the allies have refused to go along with U.S. requests to limit the sale of billions of dollars worth of equipment for the Siberian pipeline, arguing that too many jobs are at stake.

At the same time, however, it would force the Soviet Union onto a cash basis in its business dealings with the West. Some officials contend that this would, in turn, make the Soviets sacrifice resources such as gold and diamonds to pay for western imports.

One European source said that while this plan would not end future East-West business deals, it would slow them down considerably, since the Soviet Union and other East European countries count heavily on foreign credits to finance their trade.

Hermes, the West German government insurance agency, has guaranteed substantial amounts of the German bank loans for the Soviet pipeline project. And it has also guaranteed $1.8 billion of the $4.6 billion in West German loans to Poland.

An earlier proposal backed by hard-liners in the administration would involve extending the Dec. 30 sanctions against U.S. exports of equipment for the gas pipeline to European companies that manufacture such equipment with U.S. licenses.

In his letter to Reagan, the Chamber of Commerce's Lesher said that such extraterritorial controls "will only aggravate further our already poor international reputation for commercial reliability."

The letter was the strongest sign seen yet of the business community's concern over the administration's East-West trade policy. The administration has been torn for weeks between its basic sympathies for business and its desire to end the western economic relationship with the Soviet bloc.

At a breakfast meeting with reporters yesterday, chamber Chairman Donald Kendall said he "totally disagreed" with Reagan on the president's opposition to construction of the pipeline.

"Do you want economic warfare with the Soviet Union? I'm sure that's what Assistant Secretary of Commerce Lawrence J. Brady and Assistant Secretary of Defense Richard N. Perle want," said Kendall, who is chairman of Pepsico, a firm that does substantial business in Russia. He referred to two senior administration aides who have argued for tougher economic sanctions against the Soviets.

Kendall added that efforts to force European companies operating with U.S. licenses to give up sales to the Soviets could set a precedent that would hurt America's ability to conduct business internationally.

"I certainly question whether the U.S. government should put its long arm into another sovereign country and force it to accept these sanctions," he said.