The Reagan administration has backed off significantly from plans, leaked earlier this year, to ease restrictions greatly on spying on Americans here and abroad.

In a speech this week to the New York City Bar Association, Richard Willard, intelligence adviser to Attorney General William French Smith, said the administration is continuing to revise executive orders and regulations governing intelligence activities to make them "simpler, easier to apply and less restrictive of lawful intelligence practices."

Willard's speech made clear that the administration no longer supports a draft executive order, obtained in March by The Washington Post, that would have sanctioned covert CIA operations in this country.

In addition, the order would have eliminated the Carter administration's standard of using the "least intrusive means possible" to collect information, and would have restricted the attorney general's veto over such controversial investigative techniques as break-ins, mail opening, bugging and photographing.

Willard, who serves on the interagency task force drafting the new executive order, said yesterday that the original draft was never intended to be policy. He said it was put together by "middle-level people," not policymaking executives.

"One of the problems with the draft was that the wording was not as precise as it should have been . . . . It made it look as if the CIA was going to get more involved in domestic spying . . . . The language made things look worse than they really were," Willard said. "No one contemplates any changes such as getting the CIA involved in domestic spying."

However, intelligence community sources say that the draft proposal carried a cover letter signed by CIA Director William J. Casey when it was circulated internally.

In his speech, Willard said, "We are committed to the principle that intelligence agencies are subject to the rule of law and that all intelligence activities must be conducted in a lawful manner."

On the question of using the controversial investigative techniques without a judicial warrant, Willard said the administration had decided to continue the Carter policy.

That means the president must approve the type of surveillance and the attorney general then must approve the activity case by case after determining probable cause to believe the subject of the surveillance is an agent of a foreign power.

Willard indicated that the administration was going a step further in explicitly defining who can be considered an agent of a foreign power, a change the American Civil Liberties Union immediately praised.

Those who can be so classified will be officers or employes of foreign governments who are not U.S. citizens or permanent resident aliens, and any person who "knowingly engages in illegal clandestine intelligence activities, sabotage or international terrorism on behalf of a foreign power."

Willard said that, although the executive order would probably be more in line with Carter's regulations than first assumed, the final order and regulations will show changes.

"After the scandals . . . of the mid-l970s, it was thought that it was necessary to put the intelligence agencies on a tighter leash," he said. "We think it went much too far and limited the effectiveness of the intelligence agencies by subjecting them to a lot of bureaucratic regulations."

Willard said the administration also will propose legislation to tighten the Freedom of Information Act and will push existing legislation that would make it a crime to reveal the identity of a covert U.S. intelligence agent.