Foreign ministers of the nine-nation European Economic Community meeting here today finally approved the world trade liberalization package, which was completed in the Geneva-based General Agreement on Tariffs and Trade meeting earlier this year after almost a decade of intensive diplomatic efforts.

But this good news for the Carter administration, which has been pressing persistently for European political acceptance of the GATT trade package since Congress ratified the accord this summer, was offset by trade protection moves announced by the EEC tonight in response to what it believes is the "unfair competition" exerted by American chemical manufacturers on European markets.

The European protectionist measures include levying antidumping duties, which EEC's executive commission will impose "in the next few days," according to conference sources. The targets of this EEC move are major U.S. companies exporting acrylic fibers to European markets, in particular Britain and Italy.

No company names were given at today's meeting, but the two American firms involved are known to be Cyanamid Corp. and Dow Chemical Co. This follows on-the-spot inquiries by European trade protection officials of U.S. Firms' accounts earlier this month.

In Washington, a two-day meeting of high-ranking representatives of the United States and the Common Market produced a decision to turnover the fibers dispute to a meeting of trade experts.

Undersecretary of State Richard Cooper, who led the American delegation, said it was agreed that the two sides would consult under the procedures laid out in the GATT.

According to British trade Secretary John Nott, speaking here tonight, there has been "a massive acceleration of fibers into the European community generally and in particular into British markets," as a result of the break U.S. firms get from the negotiated oil prices. Petroleum is the basis for the chemical fiber industry.

The British minister was merely echoing a strongly held European feeling, most vigorously expressed by the embattled EEC chemical industry, that American oil price policy is "distorting world markets" and giving U.S. companies an "unfair advantage."

The EEC, which has had a series of unproductive meetings earlier this year with administration officials on the controversial oil price issue, clearly wants action fast, if the aggressive mood emerging from tonight's meeting proves an accurate guide to its intentions. According to Nott, European countries would have to look at the possiblity of trade safeguard measure against products like polyester and nylon yarn if the U.S. did not restrain its exports of these items to the Common Market.

What the Europeans are seeking, according to Nott, is 'a sensible voluntary arrangement with U.S." However, the timetable outlined by the British monister for achieving this appears particularly rapid to seasoned observers here.