The Dow Jones industrial average may have dropped 11 points yesterday, nipping a three-day advance in the bud, but Merrill Lynch & Co. Chairman Donald T. Regan said he has seen signs that may portend spring's "first robin as far as the stock market is concerned."

Regan told a news conference that households were net buyers of securities in 1977, if mutual funds are not counted, contrasted to their pronounced net seller statys in 1975 and 1976. He added that individual cash accounts with the country's largest brokerage firm "have been net buyers since January."

"I'm not sure it's the first robin, but it sure as hell looks like it," he said.

However, for the first quarter of 1978, Regan predicted that there would not be much umprovement over the company's hepressed 1977 earnings depressed 1977 earnings results. He noted the "poor" conditions in both the stock and bond markets for the first two months of the year, but said Merrill Lynch was profitable during both January and February. March, so far, he said, was "very good."

Regan revealed that Merrill Lynch's controversial "cash management account" program which it introduced on a trial basis in three cities last year - Atlanta, Columbus, Ohio, and Denver-Colorado Springs - would soon be expanded to the Portland - Eugene area in Oregon and to San Diego, La Jolla and Escondido in southern California.