With flights banned over Brussels and barbed wire sealing off the summit center, the 15 government leaders met to demonstrate solidarity with the United States at the highest level.

Summit host Guy Verhofstadt, Belgium's prime minister, said the leaders would seek to make their governments' anti-terrorism policies ''global and durable.''

Prime Minister Goeran Persson of Sweden, traditionally a neutral nation, came out strongly for action, underlining the breadth of the growing international coalition.

''Solidarity, that is important, that we stand united for democracy and open society,'' he said. ''We have a very strong mandate to take military action and if the United States does so, they have our support.''

Since the Sept. 11 attacks on the World Trade Center and the Pentagon, the EU nations have stood shoulder to shoulder with the United States, pledging to step up the fight against terrorists everywhere.

The leaders say the fight can only be won if it has the backing of moderate Islamic nations and is accompanied by new initiatives in the Middle East peace process.

''We have to do more than ever before to solve the problem areas that are a source of terrorism,'' said Belgian Foreign Minister Louis Michel, who was the host of a parallel meeting of the 15 EU foreign ministers.

The leaders were considering whether to send Javier Solana, the EU foreign and security chief, to Mideast capitals.

In recent months, the Europeans have criticized the Bush administration for being too aloof from the violence between Israel and the Palestinians and urged it to become more involved in the search for Mideast peace.

In his summit invitation letter, Verhofstadt also called on the leaders to calm the slumping markets.

In hectic trading, European stocks fell sharply again Friday, reflecting uncertainty about the outcome of the campaign against terrorism.

Verhofstadt asked the leaders to send a ''calm message to the markets, underlining that they are not fundamentally affected by the attacks.''

Stressing that the fight against terrorism involves more than military action, the EU leaders will seek to push forward measures set in motion after last weeks attacks on the United States.

The measures include tightening police and intelligence cooperation, clamping down on the financing of terrorist networks, improving airline security and working together to minimize the impact on the economy.