The Reagan administration yesterday praised South Africa's decision to abolish most laws prohibiting free movement of blacks as "a major milestone on the road away from apartheid."

However, State Department spokesman Charles E. Redman stressed that the white minority government's "proposals are so far-ranging and complex that we must reserve judgment on their full implications for blacks." Other department officials added that there are no plans to lift the limited economic sanctions imposed by President Reagan against South Africa last fall.

Redman also said the credibility of Pretoria's decision will depend on "quick implementation." He said South Africa should move to end "legally mandated residential segregation" and should extend the benefits of its decision to residents of the so-called independent homelands, who the United States regards as South African citizens.

President Pieter W. Botha's government announced Wednesday that it would end almost all restrictions, including the notorious "pass laws," that have been used for decades to control movement of the black majority around the country.

"Repeal of the pass laws, issuing a common identity document and other proposals . . . promise perhaps the most conspicuous discarding of discriminatory laws in recent South African history," Redman said. "It is clear that their intent is to widen the scope of freedom for all South Africans . . . . We regard these developments as an important step in the process of dismantling apartheid."

Asked whether U.S. pressure had helped produce the South African decision, Redman replied: "I can't comment as to cause and effect. You know what we have been saying for many months concerning the need to move forward with political dialogue and reform. The South African government has been saying many of the same things."