A U.S. Air Force RC135 reconnaissance plane flew "close to" Korean Air Lines Flight 007 "for a few minutes" over international waters off the coast of the Soviet Union last Thursday morning Soviet time, and at one point "crossed paths" with the Boeing 747 passenger plane, which was shot down two hours later, U.S. officials said yesterday.

But the officials insisted that Soviet fighter pilots should have known it was the easily recognizable jumbo passenger jet--and not the U.S. reconnaissance plane--that strayed hundreds of miles inside Soviet airspace over militarily sensitive areas and that there was no excuse for shooting it down.

The proximity of the two jets at one point when both were outside Soviet airspace, the officials acknowledged, may have caused some initial "confusion" in the Soviet air defense command. But they said that, by the time a Soviet Su15 jet fighter shot down the Korean Air Lines plane two hours later, the U.S. reconnaissance jet was 1,000 miles away, still over international waters.

After congressional leaders heard taped portions of monitored communications between the Soviet fighter pilots and their ground commanders during a dramatic closed-door briefing at the White House yesterday, Senate Majority Leader Howard H. Baker Jr. (R-Tenn.) said it was "clear beyond any doubt that the Soviet Union did in fact shoot down this unarmed commercial airliner."

But what remained unclear yesterday, as new details were revealed both here and in Moscow, was whether the Soviet fighter pilot who shot down the Korean Air Lines plane, killing all 269 persons aboard, knew it was an airliner, whether he told his ground commanders so, or whether the Soviets cared about any such distinction if they were aware of one.

The now-confirmed presence of a U.S. reconnaissance plane near the South Korean airliner before it strayed inexplicably into Soviet airspace has added to the complexity of untangling exactly what happened.

Soviet fighter pilots talked only of "the target" in what has been studied so far of air-to-ground communications monitored by U.S. and Japanese electronic listening posts in the region. There is no record of the Soviet pilots--at least one of whom reportedly approached to within 1 1/2 miles of the Korean Air Lines 747 in the early morning darkness--telling their ground commanders exactly what they were tracking, according to U.S. officials.

Administration sources also said yesterday that, about four hours after an Su15 fighter shot the airliner down with a heat-seeking missile, U.S. intelligence monitored communications between Soviet ground stations in which they discussed reports among Soviet pilots that a passenger plane was down and a search effort under way.

That is the first Soviet description of the plane as a passenger plane in reports studied by the U.S. government and disclosed to reporters.

Congressional leaders and government officials here have said they believe it is virtually impossible for Soviet pilots to have failed to identify the unique shape of a Boeing 747 passenger jet. But they have added that they cannot be certain that the Soviets did not make a mistake.

Sen. John G. Tower (R-Tex.) said yesterday that the Soviets were either "callous or incompetent or both, and I suspect both."

"If indeed it was a mistake, they should tell the world it was a mistake," White House spokesman Larry Speakes said of the Soviets in response to reporters' questions about this yesterday. "If they wanted off the hook on this," Speakes said, "they could at least admit they made a mistake."

The U.S. Air Force RC135 reconnaissance plane is, like the 747, a four-engine jet. But the RC135 is a much smaller plane, a military version of the older 707 airliner, and it does not have a distinctive hump atop the front of its fuselage as the 747 does.

U.S. officials said the Air Force "routinely" flies RC135 reconnaissance planes from bases in Alaska southward and just offshore along the Soviet Union's Kamchatka Peninsula, a route that passenger airliners also fly regularly.

The Kamchatka Peninsula is the impact zone for flight tests of long-range Soviet missiles. The U.S. military planes are trying to gather data on these tests to help verify whether Moscow is complying with arms control agreements. The flights are part of what is called "national technical means" of verifying such agreements.

U.S. officials said they believe Soviet ground radars were tracking both the Korean Air Lines passenger plane and the U.S. Air Force RC135. When one of the two planes started to drift into Soviet airspace, officials said, the Soviets probably thought it was the reconnaissance plane.

"It was not long," Speakes said yesterday, however, before the Soviets should have discovered they were dealing with "two separate aircraft."

After the White House meeting, House Majority Leader James C. Wright Jr., who attended yesterday's extraordinary White House briefing, told reporters that on the tapes Soviet fighter pilots twice referred to the plane inside Soviet airspace as being an RC135.

White House officials became alarmed by what they said was Wright's incorrect interpretation of what was said in the briefing. They said White House Chief of Staff James A. Baker III called Wright to explain.

Later, in a telephone interview, Wright said that what officials had said during the briefing was that the Soviets called the intruding aircraft "either an RC135 or a target needing identification" in early stages of the passenger plane's presence in Soviet airspace.

The confusion over Wright's earlier remarks led to confirmation by Speakes that there was a period early in the two-hour episode when the Soviets talked of the intruding plane as a U.S. reconnaissance craft.

Although the U.S. Air Force RC135 reportedly was far away and in international airspace throughout this episode, its now-acknowledged presence at one point along at least part of the route of the Korean Air Lines plane also is being cited in official explanations from Moscow.

Yesterday, the chief of the Soviet air defense command, Col. Gen. Semyon Romanov, said in a statement distributed by Tass that the Korean Air Lines plane had been engaged in a "deliberate" and "rude provocation." Romanov's statement claimed that the passenger jet "flew with extinguished lights and its outlines resemble much those of the American reconnaissance plane RC135."

His statement did not admit that Soviet pilots had shot down the plane. But Romanov's remarks were studied with considerable interest here.

It was the first statement on the incident to be attributed to any individual Soviet official. The fact that it came from the military air defense command chief indicated to some U.S. analysts that Moscow might be trying to separate its civilian political leaders from an action that has drawn world condemnation.

It also was the first time that the Soviets have acknowledged that the plane found in their airspace was a Korean Air Lines plane. Previously it was described only as an "intruder."

The Soviet claim that the passenger jet was flying without lights has been flatly denied by U.S. officials, who said the tape recordings of monitored communications show that the Soviet pilots reported navigation lights and a flashing strobe light common to civilian planes.

The Soviet general also claimed that "just in this year, American military planes . . . nine times violated the airspace of the Soviet Union in the region of the Kurile Islands," which lie just south of the Kamchatka Peninsula. U.S. officials said yesterday that they were aware of one incident in which the Soviets previously claimed a violation.

The Associated Press filed a story from Moscow yesterday that cited Soviet sources and reported that top Soviet military officials made the decision to shoot down the plane and that Soviet President Yuri V. Andropov, on vacation outside of Moscow at the time, was not consulted.

The news agency said the source for the story confirmed that the Korean Air Lines plane had been shot down by Soviet fighters and that Andropov had returned hastily to the capital to deal with the aftermath. The source said the decision to fire on the passenger jet was made because the Soviet military did believe that the plane was on a spy mission, the Associated Press reported.

The official U.S. disclosure yesterday of the presence of the U.S. Air Force RC135 near the Soviet Union before the Korean Air Lines plane strayed into Soviet airspace completes a set of circumstances of the kind that produces incidents.

The Soviets are well known to be hyper-sensitive about their borders and inclined to act brutally to defend them. The South Koreans, who have no diplomatic relations with Moscow, have now twice been involved in incidents in which their airliners have strayed deep into Soviet territory. In 1978, another Korean Air Lines passenger plane was shot at and forced down by the Soviets.

The region into which Korean Air Lines Flight 007 strayed is both remote and militarily sensitive, and aviators' maps warn against intrusion. It is now acknowledged that American planes routinely patrol off the coast, part of the daily cat-and-mouse game between two superpowers struggling to prevent either from gaining a secret advantage.

U.S. officials stressed yesterday, however, that none of this should excuse shooting down an unarmed passenger plane.