WASHINGTON (AP) _ Proclaiming himself ''bullish on the Philippines,'' President Reagan on Wednesday gave President Corazon Aquino another installment in money the United States has promised for her struggling government.

Reagan challenged the leaders of America's businesses to back up the U.S. government's show of confidence with private investment dollars.

Mrs. Aquino, meeting Reagan for the first time since assuming office in February, told the American chief executive, ''I hope you have set the tone and direction for a new relationship.''

Anti-Aquino demonstrators outside the White House fence shouted such slogans as ''Cory is a Communist'' while Reagan and Mrs. Aquino said their public farewells at a departure ceremony. The two heads-of-state seemed oblivious to the goings-on along the White House perimeter

The ceremony took place only a few yards from the South Lawn of the White House, where Reagan, on Sept. 16, 1982, praised then-President Ferdinand E. Marcos as ''a respected voice for reason and moderation.''

Marcos fled from Manila seven months ago after he lost a presidential election to Mrs. Aquino, widow of opposition leader Benigno Aquino. Marcos, his family and closest associates have since been living in Hawaii.

In Wednesday's ceremony, Reagan said, ''Governments, businesses, financial institutions and individuals are dealing with a new kind of government in the Philippines.''

Following the speeches of the two presidents, Treasury Secretary James Baker and Philippine Finance Minister Jaime Ongpin signed documents representing a new installment of U.S. aid.

An administration official said the aid consisted of $100 million in economic and $50 million in military aid, both approved earlier by Congress, and $10 million in emergency medical assistance which will be matched by another $10 million from Americares, a private organization.

''I'm bullish on the Philippines,'' Reagan said. ''I would hope American as well as foreign investors take notice of this incredible opportunity to help build a country.''

He said he and Mrs. Aquino discussed the idea of increasing Philippine exports to the United States through preferable trade treatment for the Philippines, and ways for that country to provide a greater share of goods and services for U.S. bases there.

Reagan also said Mrs. Aquino assured him that the military bases agreement between their two countries would be respected through its current term.

''I understand and am comfortable with her position,'' he said. ''The next review of our defense relations is scheduled in 1988, and that gives us and the people of the Philippines plenty of time to think about it.''

''Meantime, I will continue to ask Congress for appropriate levels of economic and military assistance,'' Reagan said.

The United States has given the Philippines about $500 million this year and is seeking an additional $200 million in the fiscal year beginning Oct. 1.

An administration official, who spoke on condition he not be identified, said there was no discussion of Marcos at the Reagan-Aquino luncheon meeting, which was attended by Baker, Ongpin and other U.S. and Philippine officials in addition to the two presidents.

Reagan and Mrs. Aquino also met privately in the Oval Office.

The two leaders spent half of their 45-minute meeting discussing Mrs. Aquino's strategy for ending a communist guerrilla movement against her government, said Teodoro Locsin, her counsel.

Mrs. Aquino is negotiating with representatives of the communist New People's Army and trying to institute economic reforms she hopes will wean rural Filipinos away from supporting the insurgency. She has also said that if the talks fail, she will increase military action against the rebels.

Locsin told reporters that Reagan cautioned Mrs. Aquino against trusting promises the guerrillas might make in negotiations.

''I've had experience dealing with communists and you have to be careful,'' Locsin quoted Reagan as saying.

At the same time, Locsin said the president supported Mrs. Aquino's efforts to deal with the insurgency and that both leaders ''share the same cynicism about the hard-core guerrillas coming down from the hills.''

On Wednesday night, at a black-tie, State Department dinner in Mrs. Aquino's honor, Secretary of State George Shultz told the Philippine leader, ''We are on your side. Our partnership makes an irreplaceable contribution to stability in the Pacific.''

Shultz told the Mrs. Aquino the United States was ready to help the country's economy ''in whatever way we appropriately can.''

In response, Mrs. Aquino said, ''We are a friend of freedom'' and added that the Phillipines would never again allow its leaders to ''bolt away from us.''

She cautioned Shultz that in the ''new, mature relationship'' between the two countries, the Philippines would sometimes be difficult to deal with, but she said, for the United States, a democracy, ''this should be a virtue, not a vice in your eyes.''