Gov. Harry Hughes' last black policy adviser resigned today, only four days after the firing of the governor's other ranking black assistant provoked sharp protests from legislative leaders.

Lonnie Robbins, 29, who served as Hughes' adviser on planning issues, told the governor in an afternoon meeting that he was leaving to become an assistant to Department of General Services Secretary J. Max Millstone. His departure will leave only two blacks on Hughes' staff, both in lower-level positions.

Hughes' senior aides, anxious to avoid a racial controversy over the departure of Robbins and corrections and social services adviser Josie Bass, stressed that Robbins' decision to leave was his onw. "If he wanted to stay he was welcome" said chief of staff Ejner J. Johnson.

But some members of the governor's staff said privately that Robbins, who has worked for Hughes for more than a year, was not encouraged to stay in the office. And several black legislators said they will not be satisfied unless two more blacks are hired to replace Robbins and Bass.

"I have been assured that this is not a racial situation," said Sen. Clarence W. Blount, an influential black from Baltimore City. "But I don't know what's true -- I've heard both sides. If he is not going to replace those two with other qualified blacks I'll have a problem."

According to Johnson, Hughes is currently planning to hire at least one new program aide to replace Robbins and Bass, who was fired shortly before Christmas. Johnson said that two black job applicants -- one a woman -- will be interviewed this week, "Obviously there will be a great deal of consideration given to hiring blacks to replace Lonnie and Josie," he said. "But we haven't made an absolute commitment on it."

Robbins refused to comment on reports of his resignation late this afternoon, explaining that he had not finished discussing the subject with Hughes.

Johnson, however, offered the explanation that Robbins saw better career opportunities in the Department of General Services. "There's more of a career ladder where he's going," Johnson said, "and for a young man like him, I would think that would be an important consideration."

Robbins, who earned $22,000 annually in the governor's office, will receive a small raise when he becomes Millstone's aide, Johnson said. Eventually, according to sources, Millstone plans to create a new position in his department that will put Robbins in charge of contract and procurement work.

Sources said Robbins was upset about Hughes' firing of Bass, who joined him as the first black aide in the governor's office to work on substantive policy other than minority issues.However Bass' firing did not trigger Robbins' resignation, these sources said.

After the disclosure of Bass' dismissal last Thursday, several black legislative leaders met with Hughes and asked for her reinstatement. They said that the reasons given for her falling out with other aides -- that she was a poor administrator -- amounted to "character assassination" of an intelligent and competent worker.

Those feelings were still reverberating throughout the State House today as Robbins' resignation became official. "Bass was intelligent and hard-working and one of the more competent people up here," said one Hughes aide, who asked not to be named. "She was a victim of some petty jealousies up here."

State Sen. Tommie Broadwater (D-Prince George's), leader of much of the county's black political community, said he thought Hughes had been unfair to Bass. "He could have shifted her to another position," Broadwater said. "After all, that's what they did for Mike Canning [former Hughes chief of staff], and nobody raised a fuss about that."

"I don't know who is right about Bass," said Blount, in a comment that was typical of legislators contacted. "But it all has been regrettable and unfortunate. I hope this situation doesn't repeat itself again in the governor's office."

Aides to Hughes were quick to point out that the departure of Bass and Robbins must be matched against Hughe's record of promoting blacks and black programs throughout his administration.

"I think it's more significant that the governor is going to be announcing a new Office of Minority Affairs this week," Johnson said. That new office, which will include a new staff position of executive director, will encompass the current Office of Minority Business, Johnson said.

In addition, Johnson said, he was currently reorganizing the duties of Hughes' policy aides -- including those who will be hired to replace Bass and Robbins -- to allow them a larger role in preparation of the budget and new legislation.