U.S. Steel Corp. Chairman David M. Roderick said yesterday he will file complaints alleging unfair trade practices against steelmakers in nine countries on Dec. 1, heightening tensions across the Atlantic and aggravating threats of a trade war.

Roderick told a meeting of securities analysts in New York that he will file his own antidumping and countervailing-duty complaints despite Commerce Secretary Malcolm Baldrige's announcement last week that the government will initiate unfair-trade-practices action against five foreign producers to head off more sweeping action by angry U.S. companies.

Baldrige also said that if the U.S. firms, who for months had threatened such action against European steelmakers, filed "massive complaints," he would withdraw the trigger-price mechanism because his staff isn't large enough to handle all of the work.

Under the trigger-price mechanism, prices of imported steel are monitored and, if they are sold here below specified prices, an investigation is initiated by the Commerce Department.

Last year U.S. Steel filed antidumping complaints against the United Kingdom, Luxembourg, France, Belgium, West Germany, the Netherlands and Italy that resulted in the suspension of the trigger-price mechanism. It was reinstated only after the Carter administration made some changes to strengthen the system and after Roderick agreed to withdraw his complaints without prejudice.

A Commerce Department spokesman said yesterday that the seven complaints U.S. Steel filed last year were considered "massive" enough to suspend the trigger-price mechanism, so the nine cases Roderick is threatening to file this year probably also would result in the TPM's demise. During the 1980 case, Commerce officials said the trigger-price suspension would be lifted only if the petitions were withdrawn or otherwise resolved.

During the suspension, some industry analysts suggested that European producers could flood U.S. markets with cheap steel while others said the foreign steel producers would not operate in U.S. markets for fear that a decision could be granted in the steel companies' favor, resulting in heavy duties levied against them. There were no reports of a heavy influx of foreign steel during the suspension.

A spokesman for U.S. Steel said, however, that it was his understanding that if complaints were filed after a certain period of time, the trigger-price mechanism, which protects the prices of domestic steel, would be allowed to remain.

Roderick said that he was filing his complaints because the Commerce Department's action "wasn't broad enough" and that his firm's dumping and countervailing-duty cases on five product lines will augment the Commerce Department's complaints. Together their cases will cover about 70 percent of imported steel products.

A U.S. Steel spokesman said he didn't know what countries would be named in the complaints but he said that the March 1980 complaints might provide a clue.

The European Economic Community last week denounced Baldrige's move as "a dangerous and questionable choice of action." The government-initiated cases are "one more thing causing tension," which could lead to other trade barriers by both sides, an EEC official said. The U.S. Steel complaints would be the "tail end of the position taken by Baldrige," the official said.

Roderick told the New York analysts that the company expects "difficult economic conditions" during the fourth quarter followed by gradual improvement next year, particularly in the second half. He said the company's fourth-quarter steel shipments will decline.