The truth about the American steel industry is too grim to talk about, at least during a presidential campaign in the steel valleys of Pennsylvania and Ohio.

And that's why the Carter administration's steel industry recovery plan, worked out in dozens of difficult meetings between industry, union and government officials this summer and announced at a White House ceremony last month, is not a significant factor in the final weeks of the campaign.

The silence surrounding the steel plan helps explain why President Carter appears to be fighting for survival in the old Democratic steel towns like Aliquippq, Pa.; Gary, Ind.; and Oungstown, Ohio.

The country's steel industry is in the midst of a painful transition to something smaller -- and hopefully, more modern and efficient. Since 1969, more than 100,000 jobs have been lost in the industry. e

This year's recession threw another 90,000 steelworkers out of work, some temporarily, others permanently. Although that number is shrinking, as the industry begins a gradual pick up in activity, the recall is going slowly and the jobless steelworkers face a very uncertain future.

Carter administration's steel plan does not answer the immediate problems of these steelworkers.

Its origins go back three years, to a Carter administration attempt to seek a consensus among the steel companies, labor and the industry's government regulators about the industry's survival in the 1980s.

It was not written for the election, says John Sheehan, legislative director of the United Steelworkers of America, one of the union's representatives in the three-way negotiations. (He agrees, though, that the speed of the negotiations picked up dramatically this summer, when the election began to draw near). Nevertheless, all sides recognized that any answers they found wouldn't be overnight cures. He and other participants agree.

The strongest driving force for an agreement was not the November election, but an October deadline arising from a dispute over steel imports.

Since 1977, the Carter administration had shielded U.S. steel companies with its so-called trigger price mechanism (TPM), designed to prevent foreign steelmakers from dumping below-cost steel in the U.S. in order to keep the foreign mills running and their unemployment under control.

By this year, though, the steel companies were complaining that the administration wasn't seriously enforcing the TPM, and U.S. Steel Corp. broke with the plan, filing trade suits against seven European competitors.

The Commerce Department was facing an October deadline to take sides in the dispute, and a verdict by the department in U.S. Steel's favor would have deeply fractured chances for international agreement to reduce steel output among the industrial countries, administration officials say.

When the steel plan of Sept. 30 was reached, setting up a new trigger price plan, U.S. Steel dropped its dumping suit.

The Carter plan also included a hard-won agreement between the industry and the Environmental Protection Agency to stretch out air and water pollution control deadlines on a company-by-company basis.

But it works no instant miracles.

The recession this year will push U.S. steel shipments down to an estimated 82 million tons, far below the 100 million ton production in 1979, according to industry estimates.

It is possible to increase shipments by 10 million tons next year, says David Roderick, chairman of U.S. Steel Corp. About one-third of the increase could come from reduc ed imports due to the trigger price plan, one-third from a rebuilding of steel inventories, and the rest from new business, assuming the economy recovers steadily in 1981, Roderick said in an interview.

But that is an optimistic outlook, most analysts say. A slower recovery next year, and continuing high interest rates could cut the 10 million gain in half.

On the plus side, the business tax cuts proposed by Carter would increase steel demand by 5 million tons a year by the end of 1982, Roderick said.

Some parts of the Carter program are aimed directly at the steel industry. There is special tax credit for investments by companies in economically depressed areas -- like the old steel centers -- and a proposal to give cash grants to coporations whose financial losses have limited their tax writeoffs.

In the three-way bargaining the government made clear that it wants the industry to use the tax incentives to modernize, rather than investing in other enterprises, and the steelworkers said they don't want the industry walking away from the older steel plants in the depressed steel centers of the Northeast and Midwest.

The plan empahsizes the industry's critical need to modernize. The trigger-price mechanism, for instance, will be reviewed after three years and continued only if the government is satisfied that the industry is making the investments needed to assure its long-term competitiveness, the administration says (assuming the Carter administration is still running the government then).

Likewise, the environmental concessions were qualified. The money the companies save must be reinvested in new plant and equipment, says the Environmental Protection Agency.

Modernization is a mixed blessing for American steelworkers.

Steelworkers President Lloyd McBride, speaking to a meeting on international steel issues last winter, said: "Fundamentally, our union has adopted a policy to encourage rapid investment in modernization. We are aware of the fact that an effective modernization program may result in reduced employment levels in our steel industry."

Modernization could eliminate 22,000 jobs over the next 10 years, according to industry estimates. "Nevertheless our union has endorsed the need for an agressive modernization program because the final result will be secure employment for American steelworkers," McBride said.

There is no comfort in that for the workers at the older, threatened plants in the industrial states, however.

The national steelworkers union has pushed hard for Carter against Ronald Reagan and John B. Anderson, committing about $500,000 to the campaign, according to union officials.

When plants close, or layoffs multiply, steelworkers don't want to hear about long-term solutions, Sheehan and other union officials said. The workers want their jobs back.