White House national security adviser Robert C. McFarlane said yesterday that it may take President Reagan's full four-year term to negotiate an arms-control agreement with the Soviet Union, but "the president is committed to getting results by the time he leaves office."

"We have no illusions that this will happen overnight. It will take time," McFarlane said on "Face the Nation" (CBS, WDVM).

His cautious statements were echoed yesterday in Moscow where the Communist Party newspaper Pravda, in its first commentary on the scheduled January talks between U.S. Secretary of State George P. Shultz and Soviet Foreign Minister Andrei A. Gromyko, said there still is "no sign" that the Reagan administration is prepared to take constructive steps to end the arms race.

"It's high time Washington gave up illusions" of gaining military superiority, Pravda said, according to United Press International.

The Washington-Moscow gap was illustrated yesterday by televised exchanges between McFarlane and Soviet spokesmen over a moratorium on deployment by the two superpowers of additional medium-range nuclear missiles in Europe.

The Soviet Union likely will propose a freeze or "mutual pause in deployment" of nuclear missiles in Europe, according to a report being published today in The Manchester Guardian. Izvestia, the Soviet government newspaper, last week referred to an "equilibrium" in nuclear forces now in Europe.

Vladimir Bogachev, chief military writer of Tass, the Soviet news agency, said yesterday on the CBS program that continued U.S. deployment of missiles in Europe, after the Shultz-Gromyko talks, would be seen in Moscow "as a sign of bad will . . . . What will happen later I don't know."

However, McFarlane, citing what he said was a 10-to-1 advantage of the Soviets in European-based warheads, ruled out any halt or delay in the NATO plan to place 572 American missiles in Western Europe over the next three years.

"We are looking for equality," McFarlane said, and "a moratorium on one side is not the way" to reach it.

A White House aide, expanding on McFarlane's statement, said the administration's repeated position has been that the United States would "halt or reverse deployment of medium-range missiles only in the context of an agreement, not in return for the Soviets coming back to negotiations."

The Soviet Union broke off all nuclear weapons negotiations last year after the first of the planned 572 U.S. Pershing II and ground-launched cruise missiles were deployed in Western Europe.

The Thanksgiving Day announcement of January talks to arrange for new negotiations, to include space weapons as well as nuclear missiles, has created worldwide expectation that arms control will move forward.

But McFarlane warned that talks do not guarantee results.

Referring to the SALT II treaty negotiated by the Carter administration and opposed by Reagan, McFarlane said, "This country suffered from talking in the late 1970s . . . . We learned that Soviets violate treaties. We learned that they bargain very hard, that compromise is really an alien concept to them."

Spokesmen in the two capitals appeared to offer at least an opening for possible discussions on space weapons.

Asked about antisatellite weapons, McFarlane repeated administration statements that the United States is willing "to talk about what mutual restraints are in order when the negotiations start."

The Pravda article described as "senseless" the Reagan "Star Wars" plan for developing antimissile defenses in space, and said it would threaten the existing antiballistic missile treaty.

In another area, McFarlane said the administration's plan to appoint special envoys from the two sides for the talks was raised during the Reagan-Gromyko talks in September.

He called it "one of three or four ideas which the president put out . . . as an expression of our flexibility in trying to get down to business."

Sources have described the envoys as special representatives of Gromyko and Shultz who could carry on discussions on the structure of arms negotiations if the upcoming two days of talks at the ministerial level fail to reach a final agreement.

Yesterday, McFarlane said the Reagan adminstration believes that "there might be some value in having someone who can oversee and sustain the momentum in the several talks that we think will be engendered in the coming weeks."

McFarlane also said that Paul H. Nitze, former negotiator at the medium-range missile talks, was one "of two or three that would surely qualify for such a role."

An administration source said later that Nitze may accompany Shultz to the January Geneva meeting "without portfolio" -- without official status -- and that designation of a special envoy may come after those discussions.