The new Philippine ambassador here said yesterday that while he is grateful for the Reagan administration's proposed $500 million aid package, the government of Corazon Aquino needs more access to U.S. markets and greater American investment to help it overcome "well-nigh insurmountable problems."

In his first speech since arriving here 10 days ago, Emmanuel Pelaez struck a strongly nationalistic tone. "We would like to see the United States help us in the way we need to be helped, rather than how you feel we should be helped," he told businessmen and diplomats attending a conference of the Washington Institute for Values in Public Policy.

Pelaez appealed for an economic aid program based on what he called "social justice." He called for more U.S. investment, but stressed that Filipinos must "share the fruits" of any new ventures. He asked for agricultural expertise and assistance, but "without too many imported inputs."

Calling current administration aid proposals "generous," he added: "If the American government sympathizes with us at this time -- and I have no doubt that it does -- the way to show it is to allow us better access to your markets."

Pelaez's statements yesterday seemed to elaborate on earlier remarks by other high-ranking Philippine officials, who have mixed expressions of gratitude for proposed U.S. aid increases with equally strong sentiments that the amounts are either too small or too heavily oriented toward military assistance.

Wednesday in Indonesia, Philippine Vice President Salvador Laurel said he would tell President Reagan in their first meeting that the administration's proposed $150 million in new aid was not nearly enough. Secretary of State George P. Shultz said yesterday after the meeting that Laurel "gave the impression that his needs were infinite."

Pelaez put the Philippine need for aid in the broader context of market access and technological assistance. For example, he said Reagan should temporarily increase the current quota on imported Philippine sugar to give farmers time to diversify into other products.

The Philippines, like countries of the Caribbean basin, have been hard-hit by tough new U.S. import quotas aimed at protecting growers in Louisiana and Hawaii.

Pelaez also said the Philippines' 2.5 percent share of U.S. garment imports should be increased to make it competitive with the larger shares from other Asian nations.

Pelaez said the United States could help put a dent in the Philippines' 20 percent unemployment rate by using Philippine labor and materials in constructing new housing facilities at U.S. military bases. Plans call for prefabricated components to be shipped to the Philippines for assembly, but Pelaez said using Philippine workers for on-site construction "would be providing thousands of our people with jobs."