The Commerce Department is "willing and ready" to file dumping and subsidy cases against European steelmakers as soon as the U.S. steel industry can show that it is being injured by the unfair trading practices, Commerce Secretary Malcolm Baldrige said yesterday.

The steel industry may be able to present its proof "very quickly," possibly by the end of the month, Baldrige said. "As soon as the steel companies tell us they can prove injury, we will self-initiate," countervailing duty and dumping cases, Baldrige testified yesterday at the House Ways and Means trade subcommittee.

The chairmen of Republic Steel Corp. and Bethlehem Steel Corp. said in interviews late yesterday that they would be glad to supply him with any information he needs to self-initiate the complaints.

Republic Chairman William J. De Lancey said his company definitely will file subsidy cases against the Europeans, but it will take several months to gather the necessary data. Bethlehem Steel Chairman Donald H. Trautlein told the Senate Steel Caucus that he would be ready to file antidumping cases against five product lines of six European countries after Nov. 20. But Trautlein didn't say whether his firm had decided to actually file the complaints.

De Lancey said he will provide Commerce with proof of injury within a few weeks. Trautlein said during an interview that firms "should not have to scour the world for evidence" but that the government should do it.

Dumping requires proof of injury to the domestic industry by the sale of imports at prices below the cost of producing them. Subsidy complaints must show the U.S. industry was hurt because imports were subsidized by their governments. Both types of cases are investigated by the International Trade Commission and the Commerce Department and could result in stiff duties levied on the imports.

To prove injury, an industry must show that imports were dumped, took away market share from U.S. competitors, and helped U.S. firms' profits decline.

Baldrige said that before Commerce takes any action against the Europeans they must be sure they have a strong case. "Nobody--they or we--wants to bring a case and not win it."

Baldrige would not specify which European Economic Community countries would be targets of complaints, but he said Japan and Canada would be excluded.

The EEC has said if Commerce initiates an action against its steelmakers it would be considered a hostile gesture. Steel, an EEC official said, was Europe's No. 1 trade problem with the United States.

Last August, steel imports were 62 percent higher than the previous August. Since March, imports have increased steadily from 12.3 percent of the U.S. market to 24.7 percent in August at the same time total consumption dropped. During September, Baldrige said, imports dropped 25 percent from August levels.

Baldrige also said that a large number of imports were in semi-finished shape such as oil drilling tubing and pipe, which the U.S. industry is unable to produce in large quantities. If those two products were eliminated from import figures foreign steel would only be up 2 percent, Baldrige said.

Baldrige, returning from a trip to Japan, also said unless Japan opens its markets more, the American public and Congress may create a "rising wave of protectionism."

"Despite some encouraging growth in U.S. manufactured exports over the past three years, the outlook for 1981 and 1982 is for increasing deficits," Baldrige said. This year "is expected to be worse than 1980 and 1982 to be worse than 1981."

Treasury Undersecretary Beryl Sprinkel said during testimony following Baldrige, that the 1981 trade deficit will be at least as large as the 1980 deficit.