Bob Strauss is calling to pass on a message.

"The president said this to me -- and he knows I'm going to repeat it," Strauss says. And with that the special trade representative provides what turns out to be, after weeks of silence, President Carter's first statement on the substance of Billy Carter's recent anti-Semitic remarks. He Quotes the president as saying:

"I am terribly concerned with the whole situation of Billy, including his health. You know, Bob, I just totally disassociate myself from his comments. They are objectionable and foreign to everything about the way we live our lives."

So it is, in this unusual and indirect way, that the president has moved to end his controversial silence on the matter of brother Billy and the anti-Semitic remarks.

For Jimmy Carter, the whole Billy Carter affair has become a very painful thing, personally and politically. He has been caught between the conflicting interests of his concern for his brother and his role as the leader of the nation.

While Carter talks only generally of his concerns for his brother's health, other presidential advisers go further.They say they believe the president's concern is that Billy Carter is in poor physical and emotional health, that he may well be an alcoholic. One adviser said Billy's health problems may be severe enough to require professional attention.

There was a time when the problem of what to do about Billy just involved comments and antics of general run-of-the-mill obscenity and bad taste. But, in recent months, Billy has taken to serving as an emissary of goodwill and all-American foil for representatives of the most radical of Arab states, Libya, which has given shelter and support to a number of international terrorist groups.

"There's a hell of a lot more Arabians than there is Jews," Billy Carter has said in defense of his efforts on behalf of the Libyans. And when asked this month about the criticisms that this triggered from American Jews, Billy Carter was quoted as saying: "They can kiss my -- as far as I'm concerned now."

For weeks, the president had rejected suggestions from his staff that he publicly repudiate Billy's comments. which had been widely interpreted as being anti-Semitic.

He had opted, instead, for the sort of bland comments that he gave to NBC's John Chancellor during an interview a month ago: "Well, you know, family matters and my brother, Billy, are fairly sensitive with me. Billy is an extremely independent person. Any criticism that I might make publicly of Billy would cause, I think, him to react very strongly and to reexert his independence.... I hope the people of the United States realize that I have no control over Billy; he has no control over me."

Says Strauss: "The president was in an exceedingly difficult position. On the one hand he had a sense of responsibility to a brother whom he loves and cares about. And on the other, he had a responsibility to the people in this country."

Presidential advisers who do not want to be quoted by name put it more firmly. "If Billy was well he wouldn't say that sort of thing," said one. "But the president just doesn't want to hurt [his] brother."

The president's failure to rebuke his brother brought him under increasing criticism.White House officials say that a number of prominent American Jews had let them know that they regarded Carter's silence as countenancing Billy's comments.

Meanwhile, Republican National Committee Chairman Bill Brock took the president to task for not expressing public disapproval of what he called "disgusting anti-Semitism."

Inside the White House there was also discontent. "It's pretty goddam outrageous, the things Billy is saying," commented one insider.

White House officials found themselves in the thorny position of knowing that the president's failure to repudiate his brother's comments publicly was hurting him politically, but feeling that they could not really press the matter on the president because of his feeling that the issue was a family affair and that he would hurt Billy.

Eventually, they settled on a repudiation that would be public, though once removed. Carter on the phone to Strauss; Strauss on the phone to a reporter.

Back in the days of the 1976 campaign, Billy Carter was seen as a distinct political asset for brother Jimmy. Billy served as the Carter family's ambassador to redneck America. With his praise of George C. Wallace and his fondness for "nigger" jokes, he helped keep the family on good terms with conservatives of the Deep South while candidate Jimmy was praising Martin Luther King Jr. and courting moderate and liberal America and especially the black vote.

On election day, Jimmy Carter won because he "arried the solid South, which Democrats had not done in a long time. Carter carried the South with both a large black vote (which previous Democrats had also received) plus a greater support from southern whites than orevious Democratic candidates had received.

Billy was the family good old boy, redneck was chic, and his drinking was always good for a laugh. "Billy has been concerned about the economic problems of the country," Carter joked during his first year as president. "He has pretty well put the beer industry back on its feet, for instance."

But Billy Carter has ceased to be a political plus for his brother, and his drinking has ceased to be a matter of humor.

The president is said to be very concerned about his brother's drinking and its effect on Billy's health.

Billy Carter's recent comments have served only to emphasize a problem that has plagued Jimmy Carter ever since he first ventured into the political arena outside of his native Georgia.

Jews have never felt comfortable about Jimmy Carter. And, try as he might, Carter, born-again Southern Baptist, could never change the way things were.

There was that time during the 1976 Florida primary campaign, when Scoop Jackson showed up at Miami Beach's Temple Emanu-EI and Carter showed up at nearby Yeshiva. Jackson drew a standing-room-only crowd that packed the downstairs and even the semi-circular upper balcony. They wore yarmulkes and cheered Jackson's every word. It was like Shea Stadium on cap day.

Blocks away, in the Sunday school building of Yeshiva, Jimmy Carter also campaigned. He too wore a black yarmulka and he smiled; but he just looked like Jimmy, chief of the Mousketeers. He talked about how his close personal friend, Golda Meier, had given him a car to use when he toured Israel. But he spoke to only a handful of adults, and they listened in silence, and when it was over, none could be found who said he actually felt good about Carter or wanted to vote for him.

It went like that throughout the Carter campaign, and it has gone like that throughout the Carter presidency. Carter's problems with American Jews have been compounded by his substantive statements on "legitimate rights" for Palestinians and his difference with Menachem Begin (although many Jews in America and in Israel say much the same thing).

Jimmy Carter has always seemed forced to prove to Jews, somehow, that he is not really like those rednecks they had read about who are partial to white citizens' councils and sheets with eyeholes. And that is what is so especially difficult, politically, about the Billy Carter affair.

As one presidential aide put it:

"American Jews look at Billy as Jimmy Carter's Id."