The Reagan administration yesterday denounced as "lies and half truths" a Soviet government statement that acknowledged for the first time the downing of Korean Air Lines Flight 007 while insisting that the airliner was a spy plane that deliberately violated Soviet airspace.

At the same time, White House spokesman Larry Speakes backed off earlier statements that the United States had "irrefutable evidence" that the Soviets knew the plane was an airliner.

"That's going too far, but if they didn't know they should have known," Speakes said. "They had little, if any, room to make a mistake."

The administration's reply to the Soviet statement called upon the Soviets to make "an unequivocal apology" for downing the Boeing 747 and to pay reparations to the families of the 269 victims.

The statement, read to reporters by Lawrence S. Eagleburger, assistant secretary of state for political affairs, specifically denied Soviet charges that the South Korean airliner was flying without lights and emitted "short coded radio signals . . . that are usually used in transmitting intelligence information."

"Just as there is no indication that the Soviet fighters attempted to contact the innocent airliner using the established international procedures, there is no indication that the airliner was either aware of trying to evade the Soviet fighters, or even that it was aware of the presence of those aircraft," Eagleburger said. "Tragically, there is no indication that the Korean airliner thought it was off course."

Eagleburger added that earlier Soviet statements were, "at a minimum, grossly misleading" but that the statement issued yesterday was a "lie to the world."

Administration officials were particularly incensed by a passage in the Soviet statement saying: "We will continue to act in keeping with our legislation, which is fully in accord with international regulations. This wholly applies to the question of ensuring the security of our borders."

Eagleburger said this amounted to a declaration that the Soviets "will take the same action in the future in similar circumstances."

Defense Secretary Caspar W. Weinberger said it sounded like the Soviets were talking about enforcing not international law, but "the law of the jungle."

Despite the stern tone of the U.S. reply, administration officials acknowledged that they were making progress in their efforts to force the Soviets to admit responsibility for shooting down the plane. But this was offset, in the administration's view, by the increasing focus on the issue as a conflict between the United States and the Soviet Union.

In his nationally televised speech Monday night, President Reagan framed the issue as a contest of "the Soviet Union against the world and the moral precepts which guide human relations among people everywhere."

The U.S. diplomatic aim, pursued steadily for the past several days, has been to promote international action designed to condemn the Soviet action and temporarily deny the Soviets commercial landing rights as punishment. So far, only Canada has responded, suspending landing rights for the Soviet airline Aeroflot in Montreal for 60 days.

An administration official said yesterday that "to the degree the Soviets succeed in making this an issue between them and us" it diminishes the likelihood of international retaliation.

"If all your expectation is that they would admit they've killed 269 people, than we're making progress," the official said. "But we want a lot more than that, including an apology and restitution."

Speakes said previously that the Soviets had not taken the opportunity available to them to say that the attack had been an honest, if tragic, mistake.

But when the Soviet acknowledgment came yesterday, he responded: "It's about time they did it. It's about time they owned up to what they have done."

Speakes said that it had been "like pulling teeth" to get the Soviets to make any acknowledgments. The administration's view is that the Soviets admitted downing the plane only because the United States released tapes of Soviet fighter pilots describing the tracking and destruction of the airliner, referred to as "the target."

At the White House briefing yesterday, Speakes insisted that the administration had "irrefutable evidence" that the Soviets knew when they downed the plane that it was an airliner, but he later amended this statement with a declaration that the Soviets "had little, if any, room to make a mistake."

Speakes said at the briefing that the White House had even "more irrefutable evidence" that it did not wish to release because it would compromise intelligence sources.

All of the information on the tapes released so far reportedly comes from Soviet pilots. Speakes said that the administration also has some information from ground sources that is "unintelligible."

Meanwhile, the administration continued to insist that the mild sanctions announced by the president Monday night were sufficient response. The only U.S. action taken so far, except for denunciation of the Soviets, is suspension of three minor negotiations involving cultural and transportation agreements and a U.S. consulate in Kiev.

Former secretary of state Henry A. Kissinger said yesterday on NBC's "Today" show that Secretary of State George P. Shultz should not meet Thursday with Soviet Foreign Minister Andrei A. Gromyko in Madrid, where they are to attend a 35-nation conference to review the 1975 Helsinki accords.

"I think it sends the wrong signal to the Soviet Union," Kissinger said. "After all, Gromyko is coming here in two weeks."

Kissinger said it is important for the United States to avoid giving the Soviets "the belief that we are so eager that they can hold out in arms negotiations or that they can challenge us with impunity."

Meanwhile, Senate Minority Leader Robert C. Byrd (D-W.Va.) said he had talked to Reagan after Monday's speech and received a "receptive" response to his proposal for international sanctions on grain sales to the Soviets and perhaps other trade issues.

Byrd's proposal calls for the United States to consult with Canada, Australia and western European countries to see if they would join the United States in a grain embargo. The administration has ruled out a U.S. embargo, however, and the new legislation establishing a long-term grain agreement with the Soviets prohibits such action.

Byrd said that Reagan told him he would pursue the idea with his staff, but an administration official threw cold water on the idea yesterday, saying that "grain embargos have not worked in the past, and there's little reason to think they would now."

Reagan opposed the grain embargo imposed by President Carter in response to the Soviet invasion of Afghanistan and, in 1981, lifted it over the opposition of his secretary of state, Alexander M. Haig Jr.