The Reagan administration yesterday scrapped Carter-era restraints on sales of U.S. weapons and military equipment to friendly countries.

James L. Buckley, undersecretary of state for security assistance, charged that the restrictions imposed by Carter -- involving human rights considerations, nuclear proliferation and unwillingness to be first in introducing new arms into a region -- "substituted theology for a healthy sense of self-preservation."

The restrictions were part of "an American withdrawal from world responsibilities" leading to Soviet military superiority, he added.

In a speech to the board of governors of the Aerospace Industries Association in Williamsburg, Va., Buckley said the present administration views arms sales as "an important adjunct to our own security . . . and facilitating access by American forces to military facilities abroad."

"We remain dedicated to the goal of mutual restraint in arms transfers," he said. "What we advocate is a similar dedication to the goal of serving U.S. interests; and, in those cases where arms transfers are the best means of doing so, we will make them."

Buckley said a policy statement clarifying details of the Reagan approach will be issued shortly. After sharply criticizing the Carter policy as an "escape from reality," Buckley sketched the main principles to be applied to arms sales by the new administration.

He described them as "enhancement of the state of preparedness of our friends and allies, revitalization of our alliances, the fashioning of more coherent policies and strategies that bear on East-West relations and the buttressing of our own defense production capabilities."

Buckley noted that one of his first actions after taking office was to rescind Carter's so-called "leprosy letter," which instructed U.S. officials abroad not to assist American businessmen selling arms.

"Henceforth, U.S. government representatives overseas will be expected to provide the same courtesies and support to firms that have obtained licenses to market items on the U.S. munitions list as they would to those marketing other American products," he said.

Buckley also asked for support for the administration's request that Congress authorize special, low-interest loans for selected countries that otherwise cannot afford to buy U.S. weapons.

In its proposed fiscal year 1982 budget, the administration is seeking big arms-purchase credits on so-called concessional terms for several countries in the strategically important Mideast and Indian Ocean regions.