While satellite pictures of the Soviet brigade in Cuba were being analyzed in Washington, the president of the United States was floating down the Mississippi aboard the old paddlewheeler, the Delta Queen.

Jimmy Carter didn't need any more bad news. His U.N. ambassador, Andrew Young, had just resigned in a flap over Young's contacts with the Palestinians. That incident set off recriminations between American blacks and American Jews.

Robert Strauss, Carter's Middle East envoy, was in a jurisdictional dispute with Cyrus R. Vance, the secretary of state, and Zbigniew Brzezinski, the national security affairs adviser.

There was the continuing bad news from the public opinion polls; his energy program and his SALT pact were embattled in Congress; there was lingering fallout from the Cabinet shakeup.

It was not until Aug 23 that the president was informed about the brigade in Cuba. That day he was in Hannibal, Mo., where he reminisced about the Mark Twin era.

The night before, press secretary Jody Powell had explained that the president was on top of his job and that "it doesn't mean a damn bit of difference where the president is -- in the White House or on the banks of the Mississippi."

In any case, the report on the brigade reached Carter as part of the daily intelligence briefing he received from the CIA.

The information was sent to Carter via a mobile communications center set up on the Delta Queen. It was a secure communications channel.

Carter sent word back to Brzezinski in Washington that all of the information on Soviet ground forces in Cuba should be assembled and that an interagency meeting should be held at the White House to discuss the matter.

Almost a week later, that meeting was held. As a senior administration official recalls it, it was of no importance that it took so long to pull together the military, intelligence and diplomatic records and data.

"This was something of significant concern to us," he said, "but it was not a matter of imminent crisis or danger. The troops had been there for some time. It was just that now we had to address it diplomatically."

The group that met in the Situation Room in the basement of the White House consisted of top-level officials from the intelligence community, the State and Defense departments and the National Security Council.

For the officials gathered around the table, it had already been an August far more eventful than they had envisioned or wanted. Vance had been forced to interrupt his vacation for a quick 24-hour visit to Washington to see Strauss, Vice President Mondale, and Brzezinski in a meeting that was part show-and-tell and part showdown.

Now, on Aug. 28, Vance was back again, his vacation officially over, and awaiting him was the diplomatic snarl over the Soviet ballerina who was sitting on an Aeroflot airliner grounded at New York's Kennedy airport, and the undiplomatic snarl of details in Time magazine about the in-fighting of Strauss and Brzezinski versus Vance, which infuriated the secretary of state.

For Vance, the Soviet brigade in Cuba was the issue of first priority. The officials decided to press the matter through diplomatic channels.

On the afternoon of Aug. 29, Under-secretary of State David D. Newsom called Soviet Deputy Ambassador Vladillen Vasev (Soviet Ambassador Anatoliy Dobrynin was on home leave in the Soviet Union.) Newsom told Vasev that the United States had conclusive evidence of the presence of a Soviet combat brigade in Cuba, and that this was a matter of great concern to the United States. He said that Vance would want to address the matter with Dobrynin upon his return.

In conjunction with the Newsom-Vasev meeting, officials at the U.S. diplomatic interest section in Havana were directed to take the matter up simultaneously with the Cuban foreign ministry. But it turned out that the U.S. section chief in Havana, Wayne Smith, was unable to obtain an appointment with the Cuban officials until Sept. 1. By that time the presence of the brigade had become public knowledge.

Carter administration officials initially had planned to postpone the disclosure of the brigade, hoping to deal with the matter first through quiet diplomacy. "There was never going to be a way to hold it," said one official, "only a question of whether you could hold it temporarily until you had a reply from the Russians. If so, you would have been able to go to the public with some disturbing news but some Russian reply."

But this was not to be.

On Aug. 27, the National Intelligence Daily, a classified U.S. government document with a daily circulation to several hundred officials with top security clearance -- including the Senate and House Intelligence committees -- carried an account of the confirmation that the Soviet brigade was operating in Cuba.

On Aug. 30, in the State Department an interagency meeting of undersecretaries and assistant secretaries was held to decide how and when the matter should be made public. They decided that a few key members of Congress would be informed later that day and that the next day, State Department spokesman Hodding Carter would announce, in a manner that would convey concern but no sense of crisis or alarm, that the presence of the Soviet brigade had been confirmed and that U.S. concern had been expressed to the Soviets, and that the diplomatic negotiations were proceeding.

The State Department spokesman would handle it rather than the White House press secretary because the Carter officials agreed this would help keep the matter relatively low key so that it would not be viewed as an issue of crisis proportions. "The idea was to keep the president away from it," said one administration official.

But events moved faster than did the administration. For on the same day that the officials were discussing how to make the information public, a representative of Aviation Week magazine queried both the departments of State and Defense about the confirmation that a Soviet brigade was in Cuba, an action indicating that the publication had a detailed account of the intelligence report.

That afternoon, Undersecretary of State Newsom began contacting members of Congress.

He called Sen. Richard Stone (D-Fla.), who had been raising questions about the presence of a Soviet brigade in Cuba more than a month ago. Stone, who was home in Tallahassee at the time, recalls that Newsom told him: "We've concluded our gathering of the intelligence information and we're ready to tell you what we've learned."

But Stone says he told Newsom not to bother. "I said, 'Don't tell me; let's do it in person when I get back to Washington.'"

Newsom also telephoned Senate Foreign Relations Committee Chairman Frank Church (D-Idaho) and ranking committee Republican Jacob Javits (N.Y.), House Foreign Affairs Committee chairman Clement Zablocki (D-Wis.) and ranking Republican William Broomfield (Mich.), Senate Majority Leader Robert C. Byrd (D-W. Va.) and Senate Minority Leader Howard H. Baker Jr. (R-Tenn.). Pentagon officials contacted Senate Armed Services Committee Chairman John Stennis (D-Miss.) and House Armed Services Committee Chairman Melvin Price (D-Ill.).

Of all the calls, the one to Church is the one that will be remembered -- because it was through Church that the world would first hear of the presence of the Soviet brigade.

Church earned a reputation for being a foreign policy liberal and a dove on Vietnam; and he has been finding out now that these liberal credentials are doing him no good in conservative Idaho, where he is expected to have a difficult time winning reelection next year.

As Church recalls Newsom's call, "he said that he wanted me to know that the existence of this brigade had been confirmed. He said he wanted me to know before I read it in the newspapers within 24 to 48 hours." Church says he took this to mean Newsom thought it would be leaked to the press.And that, he says, is one reason why he decided to tell the press.

The other reason, Church says, is that it was his committee that issued the statement in July, based on testimony from Secretary of Defense Harold Brown, that there was no Soviet buildup in Cuba, a statement that certainly was misleading, in retrospect, if not untrue.

So an hour later, Church called the secretary of state. He asked for some more data and then he says he told Vance he intended to make the information public. Church says Vance's only response was: "I know you'll use your best judgment in what you say."

Church rounded up a few local reporters and invited them to join him in the living room of his home in Idaho. There he unloaded to the assembled Idaho reporters one of the year's major foreign policy stories.

His words were clearly hard line.

He called for "the immediate removal of all Russian combat units from Cuba."

Church now bristles at suggestions that he publicized the information (before the State Department spokesman could) for his own political reasons. He has seen those comments from Senate colleagues and he calls them "cheap shots."

He says: "I can't believe the president intended to keep the matter secret. I made it public because I thought it best that the information come from someone in a public responsibility, not just leaked by an anonymous source."

Meanwhile, back at the White House, presidential advisers bristle at the thought of what Church did. They see him as having set a crisis tone to a matter that deserved moderate and restrained handling.

"There is not the feeling here that the way Church behaved was excusable for our own political situation," said one senior White House official. "If he was going to put a statement out, he could have been more responsible. The way he said it put pressure on other liberal and moderate senators to match it."

President Carter was back from his riverboat working vacation and on his way home to Plains, Ga., for the Labor Day weekend, unaware at the time that Church was taking care of his foreign policy public relations for him. White House officials say they had not heard from either Vance or Church what the Idaho senator was about to do.

The next morning on Aug. 21, the president discussed the matter by telephone with Vance. The president decided to try to salvage the low-keyed approach and said that Vance should handle the matter by issuing a statement. Carter went for a walk through downtown Plains, which consists of a single row of shops, mostly devoted to selling Jimmy Carter souvenirs, and he repeatedly refused to comment on questions about the Soviet brigade, saying only that Vance would do the talking back in Washington.

Despite the low-key efforts of the president and his advisers, the tone had been set. Several days later, Church was announcing that he was postponing the hearings on SALT II so his committee could "deal immediately" with the issue of the Soviet brigade.

Some Senate liberals and moderates who supported the strategic arms limitation pact joined with more conservative SALT critics in saying they doubted the pact would be approved if the question of the Soviet brigade was not resolved satisfactorily.

Newspaper editorials around the country were sounding a hard line. The Wall Street Journal, in an editorial headlined "Exploding Cigar," suggested that perhaps the Soviets would give the United States assurances that the troops were not for offensive purposes by sewing medic patches on top of the soldiers' artillery insignia.

And the president, back on the job in Washington, concluded on Friday that his low-key battle was lost and he had to speak out before, as one aide said, "senators got so far out on a limb against SALT that they couldn't get back."

On Friday afternoon, the president strode into the press room of the White House and, as television cameras covered the event, Carter declared:

"This is a time for firm diplomacy, not panic and not exaggeration."

The president had a political problem.