A public relations firm with ties to Ronald Reagan is under scrutiny for possible violation of the Foreign Agents Registration Act through its representation of a right-wing Guatemalan pressure group.

The firm, Deaver & Hannaford, Inc., was founded by two aides to Reagan during his years as governor of California. He was a client until his formal declaration as candidate for the presidency. The firm came to national attention three months ago with the disclosure that it had written material for Reagan on the Taiwan issue while in the pay of the Nationalist Chinese.

Michael Deaver has taken leave from the firm to serve as a top aide in the Reagan campaign. Peter Hannaford is an adviser on a spare-time basis.

Last month, Deaver & Hannaford signed up Amigos del Pais (Friends of the Nation), as association of Guatemalan businessmen. In seeking to counter the country's international image as a human rights violator, Amigos has engaged at least three American lobbyist-public relations offices this year.

According to the president of one of the firms, Curtis J. Hoxter of New York, Amigos turned to Deaver & Hannaford because of the ties to Reagan and the feeling within the Guatemalan group that "unless Reagan comes in, Guatemala doesn't have a chance."

The Carter administration has pressed Guatemala's military-backed government to liberalize its rule as a means of countering the influence of leftist revolutionaries there.

Deaver & Hannaford's problem with the Justice Department involves the firm's apparent failure to register under the Foreign Agents Registration Act within the required 10 days after agreeing to represent Amigos.

The firm has offices in Los Angeles as well as here and the paperwork was delayed betwen the two, said Harold L. Aronson, who handles the Guatemalan account. According to his registration with the Senate as a lobbyist, Aronson expects to receive $10,000 a month plus $1,000 for expenses from Amigos to lobby and produce a monthly newsletter.

Aronson denied that the intent of Amigos was to form a tie to Reagan. "I'm the account executive and I'm the most unpolitical type. I work both sides of the aisle and both sides of the Capitol."

Early last month, Aronson resigned as a minority staff member for a House subcommittee to take the job with Deaver & Hannaford. He traveled to Guatemala City to sign a contract, he said, but returned without it because of complications there. He started work for Amigos early in August, though the firm delayed on attempting to register the account until Aug. 27 -- more than 10 days after the work began.

A Justice Department official said the department will seek to determine if the delay was intended to circumvent the registration act's purpose -- to make public the activities of foreign agents.

Aronson maintained that was not the case and said efforts are being made to comply.

Another Washington firm serving Amigos, Patton Boggs & Blow, already is registered under the act and is listed as performing legal and other services for the Guatemalans.

In April, when Amigos had a large delegation in Washington to attend the Latin section of the American Chambers of Commerce convention, the group hired the Hoxter firm from New York to arrange a dinner with journalists interested in Latin America.

Amigos members, including several U.S. citizens with investments in Guatemala, sought to convince the journalists that many news reports from there were distorted and exaggerated the extent of rights violations.

Hoxter, who used to represent the Guatemalan government, acknowledged that he did not register with the Justice Department for his "one-shot" Amigos job in April. That's in a gray area" of the act, he said.

Amigos has a rival group in Guatemala with similar aims, called the Guatemalan Freedom Foundation. Its lobbyist here is Mackenzie McCheyne Inc., which previously worked for the Nicaraguan government of Anastasio Somoza.

Asked to compare the two business groups, Guatemala's former vice president, Francisco Villagran Kramer, who resigned last week and took refuge in Washington, put it this way:

"Amigos del Pais is equivalent to the John Birch Society and the Freedom Foundation is even more to the right."

Villagran, a moderate who quit after failing to achieve liberalization of the government he joined two years ago, recalled that among recent Amigos efforts was the invitation of retired U.S. military opponents of Carter's human rights opponents of Carter's human rights policies to Guatemala to express those views.

Asked whether the Guatemalan business groups received government money for their often expensive efforts abroad, Villagran said that, on the contrary, the business groups provided funds to the government for such purposes.