Panama has sent former foreign minister Aquilino Boyd to Washington as a special ambassador in an attempt to ease the tensions that have brought the Reagan administration close to confrontation with Gen. Manuel Antonio Noriega, Panama's military strongman.

Boyd's arrival over the weekend came as a surprise to State Department officials, who said yesterday they did not know he was here. However, Adolfo Arrocha, acting head of the Panamanian Embassy, said Boyd -- also a former ambassador to the United States and the United Nations -- would begin today to contact U.S. officials in an effort to explain the government's position in the pro- and anti-Noriega demonstrations that have wracked Panama since June 9.

In particular, Arrocha said, Boyd will seek to counter the anti-Noriega campaign being conducted here by Gabriel Lewis, another former ambassador who is widely known in Washington political circles. Lewis was among the key negotiators of the 1977 Panama Canal treaties calling for Panama to assume control of the canal in 2000. {Panamanian President Eric Arturo Delvalle last night ordered an investigation of charges against Noriega and called for a dialogue with the opposition, but opposition leaders immediately rejected the initiative as insufficient. Details on Page A20.}

Boyd, who was foreign minister during part of the negotiations, was ambassador here from 1982 to 1984 and also was Panama's U.N. representative for more than a decade in the 1960s and 1970s.

In addition to his connections in U.S. political and business circles, he is a member of one of the "five families" that controlled Panama's political and economic life until the military seized power in 1968. Even in the intervening two decades of behind-the-scenes military rule, these families, and the political parties and mass media under their control, have continued to exert considerable influence within Panama.

Lewis fled Panama June 13 after he had tried unsuccessfully to mediate between Noriega and university students and other antigovernment dissidents demonstrating against him. Lewis has been telling administration policymakers and congressional leaders that peace in Panama depends on replacing Noriega, commander of the 20,000-member Panamanian Defense Forces and the political power behind Delvalle, a civilian.

Partly in response to Lewis' arguments, the Senate adopted a resolution on June 26 calling for Noriega's suspension, pending impartial investigation of charges that he was involved in electoral fraud and the murder of a political critic.

Last Tuesday, Elliott Abrams, assistant secretary of State for inter-American affairs, made a speech calling on the Panamanian Defense Forces to clean its ranks of corruption and prepare to get out of politics. Although he mentioned no names, his speech was interpreted as a signal that the Reagan administration believes Noriega should go.

Noriega struck back by trying to portray the unrest as part of a U.S. conspiracy to prevent Panama from gaining control of the canal. The Panamanian ambassador here, Dominador Kaiser Bazan, was recalled for "consultations"; the Panamanian National Assembly called for the ouster of U.S. Ambassador Arthur H. Davis Jr., and last Tuesday, a rock-throwing demonstration by 5,000 Noriega supporters damaged the U.S. Embassy -- causing the United States to close the consular section and library in protest.

Foreign Minister Jorge Abadia Aria subsequently said that Panama regretted the attack, and sending Boyd here with the title of "ambassador at large" appeared to be another sign that Noriega wants to avoid further confrontation with the United States.

However, what he will be able to accomplish was not immediately clear because American opposition to Noriega spans the political spectrum. Conservatives such as Sen. Jesse Helms (R-N.C.) are suspicious of Noriega's close ties to Latin American Marxist leaders, while American liberals have charged him with human rights violations and obstructing Panama's return to democracy.