President Reagan has said privately that he was not fully aware of the sweeping nature of the order he signed Nov. 1 requiring that thousands of government workers with access to highly classified information take routine polygraph examinations, administration sources said yesterday.

The order also was signed without the knowledge of some top White House officials who have opposed the tests, the sources said.

White House counsel Fred F. Fielding, one of the president's top advisers on legal issues, was among those not informed of the polygraph provisions in National Security Decision Directive 196 at the time Reagan signed the secret order, the sources said.

Disclosure of the order in news reports surprised many other senior White House aides. "The question is, who did know?" one aide asked yesterday.

Treasury Secretary James A. Baker III, a National Security Council member who objected to polygraph tests when he was White House chief of staff, was described by sources as busy with the tax-overhaul bill and not present at one of the key meetings leading to the order.

The still-secret order was devoted largely to other measures to combat espionage against the United States. Reagan apparently focused on those rather than the section to broaden significantly use of polygraphs for government workers and contractors.

Expanded use of polygraphs was advocated by Central Intelligence Agency Director William J. Casey and Defense Secretary Caspar W. Weinberger, among others. Reagan approved it after being told that the United States faces an intensifying espionage threat and must take more aggressive action against it.

Polygraphs have been used commonly in specific espionage investigations, by the CIA and the National Security Agency.

Reagan scaled back the order Friday after Secretary of State George P. Shultz threatened to resign if asked to take a polygraph. Shultz had joined Baker in opposing expanded use of the so-called "lie detector" test in Reagan's first term. When the specifics of the latest order were made public Dec. 11 in a news report, Fielding strongly urged that the order be amended.

Sources quoted Fielding as saying that, while using polygraphs might be legitimate in specific espionage investigations, it was wrong to use them for such broad screening as suggested in the order.

Other officials also said privately that they believed the order had not been adequately checked by the White House staff for legal and political implications, given controversy in the courts and Congress about effectiveness and use of polygraphs.

A previous Reagan order requiring government officials to submit to polygraphs was withdrawn in February 1984 after a congressional uproar.

While advocates say they are a useful tool in investigations, critics contend that polygraphs are inaccurate and can be evaded.

The president's order, which grew out of an Aug. 7 meeting of the National Security Planning Group, included other measures designed to combat espionage, such as tighter control on movement of Soviet and Soviet-bloc diplomats and other personnel in this country.

It also called for gradual equalization of the number of Soviet diplomats in this country with the number of U.S. diplomats in the Soviet Union.

Reagan's order would have authorized the use of polygraphs on an "aperiodic" basis, applying the tests to "all individuals" with access to three categories of highly classified information. The General Accounting Office estimated last year that 182,000 people would be subject to polygraph tests under these definitions.

Reagan's order specified that an interagency group be established to implement the order. When the group first met, the issue was not brought up, sources said.

In the second meeting, a State Department official expressed reservations, as had Shultz in earlier private meetings. At the third meeting, the group decided to wait until January to deal with the controversial issue.Staff writer Don Oberdorfer contributed to this report.