Negotiators for the European Common Market indicted yesterday they would not actively protest a plan being considered by the White House thqt automically would slap stiff tariffs, or extra duties, on imported steel sold here below a specific minimum price.

While not formally endorsing the U.S. idea, European spokesmen told administration official in conferences here they prefer the plan over others that might stringent protectionist measures. At the same time, the European said they had no plan of their own to deal with the steel problem.

The development marked a second day of high-level talks between the Carter administration and the European delegation. Officials from both sides are scheduled to cap the visit with further conferences today and a dinner tonight.

The approval of the Europeans is not needed for the U.S. to institute speed up the present timetable for processing "dumping" charges against foreign steel producers. Indeed, officails emphasized yesterday, the White House simply would order the plan without any outside negotiations.

However, Carter administration officials were hopeful that the pricing plan might serve as a model for other countries to adopt as part of an effort to push through a worldwide agreement on steel marketing to be signed by all major producing nations.

Wilhelm Haferkamps, European Commission vice president for external affairs, told a news conference here that while "it's too early to talk about" any specific proposal, he "wouldn't exclude" the possibility of discussing a minimum-price plan in the future.

And American officials confirmed privately that the Europeans, while not enthusiastic about the American idea, nevertheless did not actively complain about it.The administration is preparing the move as a step to ward off pressure for steel import quatos.

The developments came as top Customs Bureau officials told Congress they never have intiated a so-called "dumping" investigation on their own, and do not intend to, even though the law gives them the authority to act on their own.

Robert H. Mundheim, the Treasury's general counsel, said to do so would involve complex decisions and could prove costly to a foreign producer who later was found to be not guilty. He indicated the department would continue to act only on complaints from U.S. companies.

Dumping refers to the practice by some foreign producers of selling their products here at below their domestic cost of production and transportation. The practice is illegal under U.S. and international law, and is punishable - in cases where a U.S. industry is injured - by extra duties.

The Treasury has been under fire from the steel industry for lax enforcement of the dumping laws until just recently. Yesterday, John B. O'Loughlin, director of the Customs Bureau's duty assessment division, said his agency gave up on stern enforcement in the mid-1960s because "any case initiated by the Customs Service never made it anywhere."

Key administration policy makers confirmed yesterday's reports that the White House is considering the pricing plan, which would establish "reference" prices for key categories of foreign-made steel and then in effect impose temporary duties on products found selling below them.

C. William Verity Jr., chairman of Armco Steel Corp., told reporters that officials plan to compute the reference prices by calculating the cost of production for the most efficient steel makers in each separate category, and adding in transportation costs and a profit of 8 per cent.

Verity said officials have told him that, under the formula the administration is considering, import prices within 5 per cent of this total would be considered fair. On others, the Treasury would impose temporary duties and seek prompt assessment of injuries to domestic producers.

High administration officials confirmed yesterday that the formula would be set unilaterally by the U.S. and would not be negotiated with foreign governments. The proposal could be put into place under the existing 1974 trade act, without need for new legislation, according to officials.

The proposal is part of a three-pronged package being prepared by a special administration steel task force headed by Anthony M. Solomon, undersecretary of the Treasury for monetary affairs. The remainder of the program is expected to include tax breaks for the industry and measures to delay pollution-control requirements.