The Reagan administration agreed yesterday to investigate the majority of the charges of unfair trading practices filed by the nation's major steel companies against 11 foreign steel makers, initiating the first step in what could be a politically tense year for the United States and its European allies.

Commerce Department officials accepted all the complaints filed by U.S. Steel Corp. and Bethlehem Steel Corp., and some of those filed by Republic Steel Corp., joined by Inland Steel Co., National Steel Corp., Jones & Laughlin Steel Corp. and Cyclops Corp. One case against the United Kingdom was withdrawn by U.S. Steel. A department official said none of the 11 countries named in complaints by the nation's seven largest steel makers were spared an investigation. Those countries were Belgium, France, Italy, Luxembourg, the Netherlands, the United Kingdom, West Germany, South Africa, Brazil, Spain and Romania.

Of the 132 cases filed by the U.S. steel makers, the Commerce Department said 109 warrant investigation, 16 were withdrawn by the steel companies and 7 were dismissed. The investigations could result in stiff duties against the offending countries in addition to disruption of trade pending final decisions by the Commerce Department and the independent International Trade Commission, which must now determine whether imports in the accepted cases injured U.S. steel makers.

Some of the cases were dismissed or withdrawn because the levels of imports involved were too small, the department official said. However, some cases with small, but slightly higher, levels of imports were sent on to the ITC to determine if they were significant enough to injure domestic steel companies.

Four of the cases dismissed were against steel bars from the Netherlands, two were against steel sheet from Romania and one against steel bars from Luxembourg, the department official said.

The decision will be high on the agenda of meetings here next week between three European Economic Community commissioners and U.S. government officials, including U.S. Trade Representative William Brock, an EEC spokesman said. The meeting will be a continuation of talks held in London last December by Brock, Secretary of State Alexander M. Haig Jr. and EEC officials, primarily to discuss steel trade and ways to prevent trade tensions from spilling over into the political arena. The EEC had no immediate comment on the administration decision but it has said its member countries are innocent of all charges.

Steel industry experts have predicted mass disruption of trade and retaliation by the Europeans as a result of the steel complaints. But U.S. government officials have said they hope that will not happen. EEC officials have said that steel trade may be disrupted but they hope some resolution can be worked out.

The foreign countries were accused of violating U.S. trade laws by subsidizing their weak steel industries and allowing them to sell steel here at prices below fair market values. In the process, foreign steel makers injured the U.S. steel industry, aiding in the loss of 76,000 steel jobs, the American firms contend.

The EEC official said the situation afflicting American steel makers isn't critical.

A critical situation would arise "if I saw my industry being taken over by some nasty characters, dumping and depriving me of the fruits of my hard labor," the EEC official said. "The facts do not corroborate this."