The administration's long-awaited plan to protect the American steel industry from low-priced, unfair foreign cmpetition goes into effect today.

The program sets minimum prices for foreign-made steel products and if an import comes into a U.S. port at a price below the minimum price, an immediate investigation will be launched by the Treasury Department to determine if the products are being dumped, or sold below fair value.

Reaction to the Carter proposal has been mixed. Several major steel companies - though not the U.S. giant U.S. Steel Corp. - have said the trigger prices are too low to protect domestic producers.

Privately, however, many steel executives admit that the trigger prices are higher than they expected. Executives such as Edgar B. Speer, chairman of the U.S. Steel Corp. and head of the industry trade association, have taken a wait-and-see attitude on the program.

They have been pressing their own independent anti-dumping cases in the Treasury Department and will continue them if the hurry-up procedures in the administration plan do not appear to be working.

Many steel importers, on the other hand, are concerned that the trigger price mechanism will dry up too many steel imports, which have served as the main check on domestic steel prices in recent years.

Anthony M. Solomon, the Treasury Under Secretary who directed the task force that developed the trigger price program, said that the government has no pre-set goal for reducing imports.

The trigger prices based on the cost of production of Japanese producers (reportedly the lowest-cost in the world) plus the transportation and other charges Japanese makers must incur in shipping their products to United States ports.

U.S. seel producers have always claimed that they could compete in the domestic market with any of the world's steel markets, including the Japanese, provided those foreign makers did not sell steel below cost.

If that is the case, administration officials say, then the Carter program eliminates any injury by foreign competitors to U.S. steel makers.

Solomon has said that if U.S. producers do not raise their prices too much, but seek to boost profits by increasing their volume, the program will sharply reduce imports. If, instead, U.S. producers try to use the program as a cover to raise prices, the trigger prices will not reduce imports as much as steel makers want them to.

The Treasury is still computing trigger prices on items that account for about 25 per cent of the total volume of steel imports, but has chosen to put a program into effect rather than delaying until trigger prices are computed for all steel imports.

Treasury officials said yesterday that trigger prices for many of the remaining products will be announced late this week.

While most attention has focused on the administration's import program (the industry claims that low-priced imports are its biggest problem), the Solomon task force also proposed other methods to help modernize steel plants and help them put in needed anti-pollution equipment.