WASHINGTON (AP) _ Connecticut Sen. Christopher J. Dodd, who helped win a pardon for Eugene Hasenfus from Nicaragua's president, has been interested in Latin America since serving in the Peace Corps in the Dominican Republican for two years in the mid 1960s.

The 42-year-old Dodd is fluent in Spanish and often forgoes the services of an interpreter when meeting with political leaders from South and Central America.

Dodd, son of the late Sen. Thomas J. Dodd, is a Democrat who has been a leading congressional critic of President Reagan's Central America policy, including aid to the Contra rebels.

He was re-elected last month to a second term and will be taking over as chairman of the western hemisphere subcommittee of the Senate Foreign Relations Committee when Congress reconvenes in January. He was in Nicaragua as part of a fact-finding trip to Central America that began Dec. 7.

Before leaving for the trip, Dodd told reporters that Nicaragua's actions in the next few months would be a major factor in whether Congress votes to renew aid to the rebels seeking to overthrow the Sandinista government.

''Certainly what Nicaraga does in the coming weeks will be watched,'' Dodd said then.

The Nicaraguan National Assembly agreed to President Daniel Ortega's request Wednesday to pardon Hasenfus, and late in the day, Hasenfus and Dodd took a plane to Guatemala.

Dodd was the chief sponsor of a 1981 law that prohibited Reagan from continuing aid to El Salvador unless Reagan certified that country was making human rights, social and economic reforms. Reagan pocket-vetoed an extension of the certification law in 1983, but the election of moderate Jose Napoleon Duarte to the Salvadoran presidency the next year lessened Dodd's concerns for that nation.

Dodd also was in the national spotlight in 1983, when congressional Democrats tapped him to respond to one of Reagan's nationally televised speeches about Central America.

He has been an active participant in the Foreign Relations Committee and on the Senate floor in campaigns to defeat military aid to the Nicaraguan rebels.

Dodd was elected to the House in 1974 and moved to the Senate in 1980, defeating Republican James L. Buckley for the seat that opened because of the retirement of Democratic Sen. Abraham Ribicoff.

He won re-election easily last month, picking up nearly 65 percent of the vote in a race that pitted him against Republican National Committeeman Roger Eddy, a former state legislator.

In Connecticut, Dodd is viewed as a politician who bridges the gap between the old and the new in the Democratic Party.

An early supporter of Sen. Gary Hart's 1984 presidential bid, Dodd also maintains close ties with organized labor and other traditional Democratic allies.

In addition to foreign policy, Dodd's major concerns in the Senate have been housing, banking and children's issues.