Secretary of the Interior Stewart L. Udall said Wednesday that federal intervention to block construction of three underpasses on Memorial Drive is highly improbable.

"Only infrequently can federal intervention be justified," Udall said, "and then only when the national interest is clearly and indisputably in conflict with state or local authorities."

Two weeks ago the Citizens' Emergency Committee to Save Memorial Drive sent a telegram to Udall urging him to designate the parkway a national historical site. It was believed that this would have rescued the Drive from its scheduled March, 1965 rendezvous with the bulldozers.

Group Misled

Udall, however, said that the group had apparently been misled about the power of the federal government over non-federal properties. When an area is privately owned or administered by a local or state government, Udall explained, designation as a historical site cannot prevent the administering agency from handling the property as it wishes.

Only an act of Congress could give the federal government full jurisdiction over the Drive, he explained.

Edward L. Bernays, founder of the Committee, still held hope that Udall would designate the Drive a historical site, which could be the first step toward Congressional action. "Secretary Udall acknowledged in his statement that he has the right to take over the Drive if it is of indisputable historical interest," Bernays said. "This is what we are trying to prove."

Udall stated that Memorial Drive probably lacks significant historical value, but at that time he had not yet received a 6600-word report from the Committee indicating the historical significance of the Drive and its environs. The report traces the history of the Charles from its discovery by Champlain in 1694 to its proximity to the future site of the Kennedy Memorial Library.

"If Udall does not exercise his right to declare Memorial Drive a historical site," Bernays said, "we have other means at our disposal to prevent the highway men from destroying the Drive."

In other recent Memorial Drive developments: Peter Blake, author of the controversial bestseller "God's Own Junkyard," will discuss the Memorial Drive controversy in a press conference in Cambridge Sunday. Blake's book is a scathing indictment of "the planned deterioration of America's landscape."