THE HAGUE, OCT. 27 -- Defense and foreign ministers of seven West European allies resolved today to speak with a stronger and more unified voice in military and disarmament decisions affecting their continent.

The pledge, issued in a joint Platform on European Security Interests, came in response to unease in European capitals over the extent to which U.S. and Soviet leaders retain power to make decisions vital to European security over the heads of European governments. This sentiment has increased since the U.S.-Soviet summit conference at Reykjavik in October 1986 and during the nearly completed negotiations to eliminate intermediate- and shorter-range nuclear missiles from European soil.

The ministers, from the seven nations of the Western European Union, issued the new security document at the end of two days of talks here. Foreign Minister Hans van den Broek of the Netherlands said the union's security platform was designed as "a kind of European identity card" in defense matters and arms control negotiations.

"We intend therefore to develop a more cohesive European defense identity which will translate more effectively the obligations of solidarity to which we are committed," the platform said in one key passage.

Prime Minister Jacques Chirac of France initiated the European declaration in a speech to the union's assembly in Paris last December. His suggestion reflected French concerns over President Reagan's willingness to bargain alone at Reykjavik and an idea that revitalizing the largely dormant seven-nation group could provide a useful and strictly European forum for defense concerns.

Diplomatic sources pointed out that France, as a nuclear power, would have a highly influential voice in such a forum because the United States is absent. The Western European Union, which grew from unsuccessful attempts to form a European Defense Community in the early 1950s, includes Belgium, Britain, France, West Germany, Italy, Luxembourg and the Netherlands.

In the North Atlantic Treaty Organization, the main forum for North American and European defense discussions, the United States is the dominant power. France, although a member of the alliance, withdrew from NATO's integrated military command largely because Charles de Gaulle concluded that Washington would make vital security decisions based on U.S. rather than alliance interests.

In his proposal last December, Chirac called for a "European defense charter," echoing the language of NATO. As late as last week, French officials were voicing hope that the union's document would carry this title. But several members, particularly Britain and the Netherlands, objected that calling the declaration a charter would confer too much weight on it and could leave an impression that revitalizing the union would create an alternative to NATO, diplomatic sources said.

Against that background, van den Broek told a closing news conference that better defining a European defense identity in the union is not meant to supplant NATO or set up a European bloc within NATO to oppose the United States.

Some European leaders, particularly Chirac, have voiced fear that the expected U.S.-Soviet intermediate-range missile accord could harm European security in the long run. The agreement would leave the Soviet Union with an advantage in conventional forces, Chirac has said, and could lead to Soviet proposals for a new round of negotiations on battlefield nuclear weapons or French and British independent nuclear forces.

The union's defense and foreign ministers also decided on increased coordination of their forces in the Persian Gulf area, Defense Minister Willem F. van Eekelen of the Netherlands announced. Military officers from each of the five European nations with forces in the gulf region will be appointed to keep the group working together, he said.

The Netherlands, this year's president of the union's council, sought to coordinate dispatch of European naval forces to the gulf region through the organization in August. But France and Britain, in individual decisions, sent mine sweepers to protect their warships without reference to the Dutch efforts.

Since then, the Netherlands, Belgium and, to a lesser extent, Britain have worked out extensive cooperation arrangments for their ships. Italy, the fifth European nation that has sent ships, has agreed to share information but restricts its role to protecting Italian ships, van Eekelen said.