President Carter promised the steel industry that his administration would vigorously enforce the nation's anti-dumping laws to insure that foreign countries do not sell their steel below cost in the United States.

But Carter warned a closed-door session at the White House against trying to find "simplistic" solutions to the steel industry's difficulties and said. "We can't afford to erect trade barriers around our nation."

Administration officials met with representatives of steel producers, steel unions and steel users to try to develop ways the government can aid the steel industry.

Steel executives, who have long blamed their problems on unfair competition from foreign steel makers, surprised many observers yesterday and said they do not want quotas or voluntary restraints on imports but merely the strong enforcement of anti-dumping laws that the President promised.

Edgar E. Speer, chairman of U.S. Steel Corp. and one of those attending the White House conference said the industry was not in favor of putting up barriers to imports but in better enforcement of the laws which prevent foreign producers from selling below cost in the United States, in effect exporting their unemployment to U.S. mills.

Since mid-year about 20,000 steel workers have been laid-off and several million tons of production capacity has been closed.

Rep. Charles Vanik (D-Ohio), one of 11 legislators who attended the session, said he was "really shocked at the rather relaxed compacency of the President of U.S. Steel," about the need for import restraint.

Vanik, chairman of the foreign trade subcommittee of the House Ways and Means Committee, said some temporary restraints on steel imports are needed. Japan and some European producers have said they would be willing to woluntarily curb their shipments of steel to the United States.

In return they want the U.S. government to discourage steel companies from filing anti-dumping complaints, a procedure which now appears to be the cornerstone of the administration's plan to deal with the problems of steel imports.

Lloyd McBride, president of the United Steel Workers, told reporters after the session that he had confidence in the long-range plan to prevent foreign producers from dumping their steel on the American environment.

"In the long run the industry has said it can compete" with anyone as long as the competition is fair, McBride said. "I accept that. I think it's true."

However, he said, in the near-term there remains a severe import problem that will not be dealt with by more vigorous enforcement of trade laws.

McBride said later that he is "more concerned with not having any more steel mills close or any more steel workers laid off." He said that temporary uotas are needed "so we can better take care of ourselves in the interval" between now and when the longer-range program takes effect.

Carter, who attended the four-and-a-half hour session for about 45 minutes, told the group that it has just come to his attention that the nation's anti-dumping laws "have not been vigorously enforced," which he called a "derogation of duty" on the part of the government.

"We're going to do something about it," he promised.

Robert S. Strauss, the President's chief trade negotiator, told reporters after the conference that much of the industry and labor criticism of the government has been valid for the last 10 or 12 years.

"The government has not been sufficiently aggressive in pursuing the remedies available," he said.

Treasury Secretary W. Michael Blumenthal has promised that dumping complaints by steel and other industries will get expeditied action by his agency.

A sweeping dumping complaint was filed by U.S. Steel last month, charging that Japanese producers are selling five major product lines, worth about $2 billion, at below cost.

Blumenthal said the Treasury will take initial action on that complaint in less than the 30 days required under the law. The 30 days are up next Thursday.