By JAMES HOOKWAY

HUA HIN, Thailand -- Leaders of Southeast Asia's struggling economies met on Sunday to urge major trading partners, such as the U.S. and the European Union, to continue opening up trade, even as many countries in the region grapple with protectionist legacies amid the global economic slowdown.

The 10-member Association of Southeast Asian Nations signed a free-trade agreement with Australia and New Zealand on Friday during its annual summit to add some meat to its pitch, which it intends to take to the Group of 20 nations' meeting in London in April. The pact with Australia and New Zealand, to take effect in December, is projected to expand trade among the 12 countries by $48 billion by 2020. But Asean leaders say they are eager for more.

Thai Prime Minister Abhisit Vejjajiva, who hosted the summit, on Saturday urged Asean to take the lead in resisting protectionist policies. "If we start going down the route of protectionism, everybody will go down. It doesn't help anybody at the end," he said.

Several Asean members -- notably Thailand, Malaysia and Singapore -- are heavily dependent on exports. Since the onset of the global financial crisis, they have seen their economies contract or sharply slow as the economic situation in the U.S. and other major nations deteriorates.

Indonesian Trade Minister Mari Pangestu said in an interview on the sidelines of the summit that the world's biggest trading powers need to re-engage in the stalled Doha round of free-trade talks at the World Trade Organization "as soon as possible" to help offset a deeper global downturn. Ms. Pangestu noted that none of Asean's member nations had adopted tougher trade barriers in response to the onset of the global crisis last fall.

But some countries in Asean are turning to other, nontariff measures to aid their local businesses, sometimes at the expense of foreign competitors. Malaysia, for example, offers companies based there financial incentives to lay off foreign workers instead of Malaysians.

Write to James Hookway at james.hookway@awsj.com