Dan Rather immediately postponed his vacation when he learned yesterday a South Korean commercial airliner had been shot down by the Soviets, but President Reagan delayed interrupting his. The president's face was conspicuous by its absence during the daylong, unfolding coverage of the tragic and potentially inflammatory incident.

The networks were frustrated in their attempts to cover the story by an absolute lack of video from the scene of the incident or anywhere near it. Because much of official Washington is on vacation and out of town, it was also difficult to track down members of Congress for domestic reaction to the crash, one of whose casualties was Rep. Larry McDonald (D-Ga.).

CBS News Moscow correspondent Don McNeill reported early in the afternoon that the Soviets were refusing to let any stories on the incident be transmitted by satellite to the United States, claiming satellite facilities were under repair or booked for other purposes. During an earlier report on "The CBS Morning News," McNeill's telephone conversation with anchor Bill Kurtis suddenly went dead, and when CBS News producers attempted to reach McNeill, they were told no incoming foreign calls could be accepted.

The lack of access to immediate information, perhaps almost as much as the incident itself, contributed to a de'ja vu Cold War chill that dominated the day's ongoing coverage.

Reagan's first reactions were relayed through White House spokesman Larry Speakes while the president remained in seclusion on his Santa Barbara, Calif., ranch. Speakes appeared in an open-collared sport shirt and read a statement. Shortly after 5:30 p.m., Speakes appeared again, this time wearing a tie, and read another statement in which the president said, "Words can scarcely express our revulsion at this horrifying act of violence." Speakes said last night that Reagan would return to Washington today.

Just before 2 p.m., ABC News White House correspondent Sam Donaldson reported from near the ranch on the president's activities: "He'll go horseback riding this afternoon and work around the yard."

Shortly before, on CBS, Rather asked correspondent Bill Plante if the president's advisers thought it would look bad for the president to remain on vacation during such a crisis. Plante said of Reagan, "He has never chosen to leave the mountaintop and come home" during other such crises.

And later, on "The CBS Evening News," while Rather recounted the chronology of the day's traumatic events, a long-range camera showed a picture of the president riding a horse on his ranch, giving the impression that he was oblivious and uncaring even though official White House statements had been strongly worded.

Although Reagan never made a formal statement in person, former President Jimmy Carter did, just after 3 p.m., calling the incident "regrettable and inexcusable."

By midafternoon, network news organizations were not only deep into reporting the story on the air, but also deep into disputing which of them had first reported that the plane had been shot down by a Soviet fighter.

The Cable News Network (CNN) and other news organizations reported Wednesday night that the plane was missing. On ABC News "Nightline," Ted Koppel reported that the plane was "believed" to have been "forced down" on the Soviet-held island of Sakhalin and that "a U.S. congressman is apparently in Soviet hands."

At 6:30 a.m. yesterday, CNN was reporting that the plane had indeed been "shot down" but the identity of the attacker was still not known. ABC News later claimed it made the first authoritative, nonqualified report that the plane had been downed by a Soviet fighter during a special report shortly after 10 a.m. Jack McWethy, the ABC News chief Pentagon correspondent, said then that the plane had been shot down by the Soviets.

But spokesmen for NBC News say virtually the same information was conveyed hours earlier during the 8 a.m. news segment of the "Today" show. Anchor John Palmer was on the air reading the news when Jack Reynolds, chief defense correspondent, phoned the control room and told senior producer Marty Ryan that Japanese intelligence had intercepted radio transmissions from Soviet fighters and that those transmissions included the words, "You are free to fire."

Ryan relayed this information to Palmer through Palmer's earpiece and he spoke the words on the air as he heard them from the control room. But ABC News spokesmen insisted this did not constitute final confirmation of the attack.

Rather was scheduled to begin a long Labor Day weekend vacation today (tonight's edition of "The CBS Evening News" was to be anchored by Diane Sawyer) but dropped those plans when the gravity of the story became apparent. NBC News special reports on the incident were anchored by Roger Mudd, whose tenure on "NBC Nightly News" ends Friday; coanchor Tom Brokaw, who next week takes over the broadcast solo, is away on vacation.

And ABC News anchor Peter Jennings was also absent from the day's reporting because he was in New York going through camera "blocking" exercises on the new "World News Tonight" set that makes its first appearance Monday night. Jennings was back in Washington late yesterday afternoon to anchor last night's "World News" broadcast.

NBC News scheduled a special report, "Shot From the Sky," for 11:30 last night, and CBS News scheduled its own, "The Death of Flight 7," for the same hour. ABC News did not have to schedule a special report because its "Nightline" program airs regularly in that time slot.

The story was unquestionably dramatic as it evolved yesterday, even though the networks were restricted in what they could show. Secretary of State George P. Shultz, in a statement telecast live at 11 a.m., appeared even more shaken and distraught over the incident than did the widow of McDonald, Kathy McDonald, who was interviewed on CBS and other networks early in the afternoon. She said she had "just heard Secretary Shultz on TV" and that the attack on the airliner was "a typical action of the communists and the Soviet Union," the kind that she and her husband had been warning the world about.

McDonald was president of the anti-Communist John Birch Society.

Those members of Congress who did appear with reaction on the networks included Sen. Patrick J. Leahy (D-Vt.), who called the incident "cold-blooded murder," and Sen. Charles McC. Mathias (R-Md.), who spoke of "ruthless brutality."

On an expanded, all-morning version of "The CBS Evening News" beamed to the West Coast, former assistant secretary of state Richard Holbrooke suggested that in previous times, such an occurrence would have been deemed "an act of war." Holbrooke was interviewed by Kurtis, not by Sawyer, because Holbrooke is dating Sawyer, a CBS spokesman explained.

A dial-switcher checking the various stations and networks for their coverage yesterday morning, and one with access to a cable system would have noticed that while the reports continued around the dial, Home Box Office was offering the pay-TV premiere of the 1982 Warren Beatty movie "Reds."

In yesterday's Style section, former assistant secretary of state Richard Holbrooke's comment on the Korean jetliner crisis was incorrectly reported. Holbrooke, in fact, never made the statement in his interview on CBS Morning News. The account of Holbrooke's interview was provided by a CBS spokesman.