A clue to where Jimmy Carter has gone wrong is found in the rejection of 4-month-old advice that he would be "out on a limb" if new spending programs for the cities were proposed without the bureaucratic streamlining promised in the Carter campaign.

A Dec. 5 staff memorandum containing that warning is consigned to limbo. President Carter's urban plan unveiled March 27 contains not a word about reorganizing the inefficient, sprawling bureaucracy that sprays tax money into the cities. No such plan will be offered this year. Nor is there any firm commitment for the future.

Since the mess in urban programs generally (and in the Department of Housing and Urban Development specifically) is not disputed at the White House, the reason for not reorganizing it this year is wholly political . Administration officials privately admit they dare not anger big-city mayors and black leaders in the election year.

That shows Carter following the conventional wisdom in politics that he defied in his spectacular climb from nowhere. Preoccupied with global diplomacy, he now relies for domestic strategy on the judgement of conventional politicians. So the pledge to reorganize government that helped win the presidency sinks sto low priority.

Tthat was not so clear last Dec. 5 when a staffer named Lester M. Salamon drafted a seven-page memo to his boss, Harrison Wellford, head of the the President's Reorganization Project. He warned that the evolving urban plan "lacks a coherent focus and consists basically of proposals for expanded funding of existing programs capped by a highly dubious, free-standing development bank that will do as much to contribute to the fragmentation of federal efforts as it will to promote economic growth in the cities."

"That "leaves the president out on a limb with respect to his campaign pledge to simplify and rationalize existing programs before adding new dollars or new programs to them," Salamon's memo continued. "As the institutional embodiment of those pledges, our failure to protect the president vigorously on this point could be costly."

It was too late, said Salamon, for reorganization schemes if the urban plan was released before Christmas. But they could be ready by March. Certainly there was no disputing the need: "All parties seem to agree that the fragmented, disjointed character of federal programs in this area is b big part of the problem."

"All parties" did not include HUD. The attitude there was epitomized by Secretary Patricia Roberts Harris on NBC's "Meet the Press" April 2 when asked why not one existing program was eliminated: "there were no programs that we felt at this moment should be eliminated because each was meeting a very real need,"

HUD's resistance coincided with the program review presided over by Vice President Walter Mondale to establish priorities for 1978. Mondale, a more conventional politician than the president, was scarcely the one to place reorganization above spending. "When we talked to Mondale about reorganization," one reorganizer told us, "we heard doubts about how much political freight can carry.

"We lost urban reorganization in the politics of 1978," one issider told us. Voluminous option papers presented to Carter for determining his urban plan did not mention reorganization. Nor did Wellford succeed in efforts to set a date in 1979 for reorganization.

Although Salamon's memo expressed fear that issuing the urban plan "could foreclose important reorganization options," it is not too late. Salamon argued then that the urban development bank "would run counter to the president's reorganization commitments by establishing a new entity that duplicates functions already performed elsewhere." Now, Congress may save Carter from himself by delaying action on the bank this year.

Even so, who will effectively promote this and other reorganization schemes now that Bert Lance is gone? The logical answer is the man who claimed national credit for modernizing that Georgia state government: Jimmy Carter. But even Carter sides say the president, entranced by his role of world leader, has no time for such tedium.

Filling in blank spaces on multiple-choice option papers five days before the urban plan was released, the president instinctively rejected new spending programs and then characteristically was talked into accepting them after all (at the final, chaotic meeting lasting till 2 a.m.). But there is no evidence he felt "out on a limb" without a reorganization plan. That supports those presidential aides who fear Carter has forgotten a major force behind his ascent and his brief enjoyment of national popularity.