Tunisia, stunned by the dual blows of yesterday's Israeli air raid on the PLO headquarters near here and seeming U.S. presidential endorsement of the attack, registered its dismay today with a sharp official protest and street demonstrations against its American ally.

Confronted with massive security forces, groups of youths shouting "Reagan coward," "Zionist collaborator" and "An eye for an eye, a tooth for a tooth" dispersed peacefully in early afternoon after briefly demonstrating in front of the U.S. cultural center downtown.

At the United Nations, Tunisia called on the Security Council to issue a strong condemnation of the Israeli raid and demanded reparations. Israeli Foreign Minister Yitzhak Shamir, in New York to speak to the U.N. General Assembly, told a radio interviewer that Israel would have "no political price to pay" for the raid. Details on Pages A30, A32.

The sudden and palpable anti-American mood in a country that traditionally has had close relations with the United States was fueled by the mounting death toll, which by nightfall, according to Tunisian official sources, had risen to 73, including 12 Tunisians, 8 of them policemen.

At the U.S. Embassy, marine guards wore camouflage uniforms, flak jackets and steel helmets, and staff at such outlying installations as the U.S. Agency for International Development and the American School were sent home early.

More significant Tunisian disapproval was registered when 82-year-old President Habib Bourguiba summoned U.S. Ambassador Peter Sebastian to express his "profound regret and great astonishment" at the White House characterization of the raid as a "legitimate response and an expression of self-defense." President Reagan said at a press conference yesterday that Israel and other nations had the right to strike back at terrorists "if they can pick out the people responsible."

An official Tunisian statement said Bourguiba "stressed forcefully and with insistence the need for the U.S. to reconsider its negative and unexpected position on this attack, a position which goes against international law and existing relations between Tunisia and the United States."

Despite a letter from President Reagan denying any U.S. participation or foreknowledge of the raid, the statement's wording suggested continuing doubt by expressing Bourguiba's "uneasiness and concern about the role the United States might have played" in the attack. The U.S. 6th Fleet is in the Mediterranean.

U.S. Embassy officials declined to comment on the hour-long meeting at Bourguiba's suburban palace at Carthage, which Tunisian officials said was even more bitter than the communique indicated. Western diplomats and Tunisian officials said privately that the White House statement on the raid had surprised, disappointed and embarrassed Bourguiba's government.

Since Bourguiba led Tunisia to independence from France in 1956, he has relied on U.S. protection in a number of crises and in turn has adopted a moderate position on Middle East affairs, including playing down criticism of Israel.

Faced with a volatile neighbor in Libya, Tunisia in the past five years has received increased U.S. aid, which this year amounts to $70 million for military purchases and $22 million for economic support. That support, backed by the presence of 6th Fleet ships, has been crucial since Libya expelled about 30,000 Tunisian workers two months ago.

"The Libyan expulsion of our workers was a big surprise for us," Deputy Foreign Minister Mahmoud Mestiri said in an interview, "and a bigger surprise was the Israeli raid, but the biggest surprise was President Reagan's reaction."

Some officials here privately say they are convinced that the United States was at best inconsistent in recently broadcasting its commitment to "the sanctity of Tunisian territorial integrity" when Tunisia was faced with Libyan threats but condoning Israel's violation of that integrity yesterday. But the government, which one official admitted was still groggy from the raid and the U.S. statement, appeared to have little immediate recourse but to ride out the storm.

Libyan radio broadcasts have taunted the Bourguiba government, regularly denounced as "valets of the United States," by charging that in a crunch, Washington inevitably lines up with Israel.