Saudi Arabia, criticized in Congress recently for not supporting U.S. objectives in the Middle East, has given more than $500 million to guerrillas fighting Soviet troops in Afghanistan over the last two years, according to Saudi and U.S. sources.

While the Saudis have long been known for their reluctance to take highly visible positions on such foreign policy issues, it is known that the Afghans are the only group other than the Palestine Liberation Organization allowed to have offices and raise money openly in Saudi Arabia.

In recent weeks, the Reagan administration has urged the Saudis to make public their role in support of the Afghans, and the Saudis now seem willing to do so.

Last night, for instance, the Saudi ambassador, Prince Bandar bin Sultan, held an embassy reception to honor Afghan resistance leaders visiting the United States.

One well-placed source said Reagan administration officials asked Bandar to sponsor the reception as a public sign of support for the insurgents. The resistance leaders visited Saudi King Fahd last week on their way here, the source added.

Another informed official said the Saudis gave $250 million to the Afghan resistance last year and are giving $275 million this year. That is a direct match of U.S. covert contributions to the Afghans, the official said.

Others have placed the U.S. total as far higher. The difference may be because Congress has consistently doubled the administration's aid request for the guerrillas, sources said.

A Central Intelligence Agency spokesman said it is CIA policy not to comment on reports about covert programs. The money is used to buy guns and supplies shipped to the guerrillas from neighboring Pakistan.

One source said the Saudis are willing to go public with their support for the Afghans because it shows that they are backing other Moslems in a fight for freedom. Another source said the reception was intended to send a signal to the Islamic world that the United States also "is doing something about an Islamic problem."

Others suggested that the more visible stance also is a reaction to the congressional controversy about the Reagan administration's recent proposal to sell advanced arms, including missiles, to the Saudis.

President Reagan was forced to lobby extensively to obtain the minimum 34 Senate votes needed to sustain his veto of congressional resolutions blocking the sale.

Chief among the insurgent leaders' concerns has been their need for sophisticated missiles to combat Soviet helicopters.

It has been reported that the administration has approved covert shipment of Stinger missiles to the insurgents. But sources said this week that they have not been used in Afghanistan because the resistance fighters must be trained to use them