What a difference a day -- or 90 days -- makes.

Three months ago former governor Terry Sanford of North Carolina, feeling a distinct lack of enthusiasm on the part of his fellow Democrats, announced that he would not be a candidate for the Senate seat of Republican John P. East, who is retiring for health reasons.

Sanford, however, has reversed his decision and announced that he will file for the Democratic nomination after receiving belated encouragement from delegates to the recent state party convention. According to political observers, Sanford began looking better and better to Tarheel Democrats, who see an excellent opportunity to win East's seat -- and real weakness in their other candidates.

"Last fall I thought, 'Somebody else will do it,' " Sanford said. "But it didn't work out that way."

Sanford, 67, who served 16 years as president of Duke University, hasn't held public office since he was governor from 1961 to 1965. He made unsuccessful runs in the Democratic presidential primaries in 1972 and 1976.

Sanford's decision came as a shock to one potential candidate, Commerce Secretary D.M. (Lauch) Faircloth, a long-time friend and ally, who was going to announce today. Faircloth described Sanford as a "formidable contender" and said, "I really don't know now whether I'll run."

Meanwhile, the contest for the Republican nomination between David Funderburk, the candidate of Sen. Jesse Helms' Congressional Club, and Rep. James T. Broyhill, a moderate, is reviving memories of the bitter 1984 Senate race between Helms and then Democratic governor James B. Hunt and of the bitter GOP split in the 1970s between Helms conservatives and party moderates. Funderburk has begun running ads saying that Broyhill has "voted for tax-funded abortions 14 times" and that Broyhill was the only North Carolina Republican to vote for "Tip O'Neill's budget" last year.