The Reagan administration, in a maneuver circumventing the human rights considerations imposed by U.S. law, has approved the sale of 50 2 1/2-ton military trucks and 100 jeeps to the military-dominated government of Guatemala.

The $3.2 million sale, approved without public announcement on June 5, is the first step in President Reagan's controversial move to improve U.S. military and political cooperation with Guatemala as part of a campaign to counter what the administration regards as a growing communits threat in Central America.

The once-close military ties between the United States and Guatemala have beem dormant since 1977 because of criticism by the Carter adminsitration of widespread human rights abuses in Guatemala.

Last month, however, retired general Vernon D. Walters, a special representative of Secretary of State Alexander M. Haig Jr., visited Guatemala and publicly announced the new administration's intention to help authorities there resist terrorism and guerrilla warfare allegedly fomented by Fidel Castro's Cuba.

Opening a new military supply relationship with Guatemala involves some sensitive human rights questions since Congress has barred the sale of most military equipment to governments whose records on human rights cannot pass security. In the case of the truck and jeep sale, the State Department sidestepped that problem by getting the equipment reclassified in a way that avoids that provision on the law.

Specifically, the administration, prior to approving the sale, removed vehicles of that type from the so-called "crime control" list. Under the rules decreed by Congress in 1978, items on that list cannot be sold to governments "engaged in consistent patterns of gross violations of internationally recognized human rights."

Guatemala has refused to allow its rights record to be considered as a factor in any arms relationship with the United States, and State Department officials say privately it is doubtful that Guatemala could pass the test imposed by the law.

After being taken off the "crime control" list, the trucks and jeeps were reclassified on another list of controlled military-type export items called "control for regional security." If the State Department approves, equipment on this list can be sold without taking the recipient country's human rights record into account.

Although some congressional partisans of a strong U.S. human rights policy are understood to have questioned the propriety of the administration's action, State Department officials said they believe the law gives them discretionary authority to transfer items from one list to the other. The officials also contended that the change was made not to circumvent the human rights issue but to stimulate export sales of American-made vehicles.

The Guatemalans also have been seeking to buy spare parts for Huey helicopters used by their armed forces in countersurgency operationss, and there have been rumors that the administration is preparing to meet that request.

But, department sources said yesterday, the helicopter parts come under the "munitions list," which is subject to more stringent restrictions on what can be removed by administration discretion. The sources added that no decisions have been made about meeting the request for helicopter spare parts or on the possible supply of additional weapons to Guatemala.

Instead, the sources insisted, the administration is engaged in a "watch-and-wait" process to see whether the Guatemalan authorities are making efforts toward social reform and respect for individual liberties before seeking changes in the law that would permit resumption of a full-scale military supply and training relationship.