Alex Williams, kicking off his campaign for reelection as Prince George's County state's attorney last night, was deep into his announcement when a tall man carrying a child on his shoulders edged to the front of the crowd and waved.

Williams, who was thanking his family for their support, recognized the newcomer instantly. "And we've also had support from a lot of senators and delegates and council people, and we have an additional official who has just walked in," Williams said. "From the south part of the county, the president of the Senate, Mike Miller."

This prompted more prolonged applause from Williams's 250 backers. The tall man, Senate President Thomas V. Mike Miller Jr. (D-Prince George's), one of the state's most powerful political figures, waved again.

That's how far Alex Williams has come.

In 1986, the year newcomer Williams upset 24-year incumbent Arthur A. "Bud" Marshall Jr. in a Democratic primary, Miller was on Marshall's side. "But I expect to have every elected official in this county with me this time," said Williams, who beat Marshall by only 1,800 votes in their last contest and is expected to beat him more handily this year. Marshall has announced his candidacy but has not said whether he will run as a Democrat or a Republican.

Marshall's party affiliation won't matter, said County Executive Parris Glendening, one of several figures from the county's largely white power structure who came to cheer Williams on last night.

Among the others applauding the state's attorney at last night's rally at Prince George's County Community College in Largo were state Sens. Leo Green and Frank J. Komenda, County Council member Richard J. Castaldi and Sheriff James V. Aluisi, all Democrats. Rep. Steny H. Hoyer has endorsed Williams, and Sen. Barbara A. Mikulski sent a representative to the rally.

"He has implemented programs in the office that were long overdue," said Del. Timothy F. Maloney, a Beltsville Democrat. "As a politician, he has gone from being an unknown figure who squeaked out an election in 1986 to becoming one of the three top political figures in the county."

However, interviews with dozens of lawyers, current and former employees, campaign workers and other elected county officials show that it hasn't been easy for Williams, a staid and cerebral law school professor. Williams has sometimes stumbled, they say, because of his inexperience as both a prosecutor and a politician.

His relationship with county police is tense because of the most controversial case of his tenure, the investigation of the death of Gregory Habib, a native of Ghana who died during a struggle with four white police officers. Williams upset members of his own staff when he alleged that some of them may have tried to shape the outcome of the investigation by talking to attorneys for the accused officers.

Williams is favored to win reelection. In fact, several county leaders said Williams is carefully plotting his way toward a higher office, possibly Congress in 1992 if the county gains a second congressional district, or the county executive's post in 1994.

"Alex has attempted to garner wide appeal in the community," Maloney said. "If he continues along that line, he should have no problems in the future."

In the 1990 version of Williams vs. Marshall, Williams will have many of the same campaign advisers. But missing from the team will be lawyers Tom Farrington, Wayne K. Curry and Gregory Wells and James Pringle, who was a key strategist.

Farrington's exit typifies what some see as Williams's inexperience as a politician. "After the {1986} election was over, I did not hear from Williams for six months," Farrington said. "It goes beyond a lack of political skill. It goes to thoughtlessness."

Williams said he thought that he had thanked Farrington. "Maybe protocol would suggest that I bring him in and thank him and thank him again," Williams said.

Some would dismiss the Farrington episode as a matter of a bruised ego. But others who have worked with Williams's campaign said that it is evidence of Williams's political naivete.

"Sometimes after fund-raisers, we'd have to remind him of who to call and thank, and he wouldn't always do it," said one of Williams's campaign workers. "It was never deliberate. He's still evolving as a politician."

Williams "grew apart, philosophically," from Curry, Wells and Pringle on how he should use his position as the county's most visible black elected official, Williams said.

They saw Williams's election as an opportunity to create a 1990s version of a political boss who should use his prominence as the highest-ranking elected black official in a county that is 50 percent black to secure political and economic gains for his natural constituency. But that was a role Williams repeatedly has said he will not assume.

"The people who want Alex to be a certain way and criticize him are those who would divide the county along racial lines," said Peter Krauser, chairman of Williams's campaign committee.

The philosophical differences between Williams and some of his close advisers -- both current and former -- were apparent even before his inauguration. Some of them told Williams that some people who had worked for Marshall should be fired.

"He did not do it, and I think he paid for it," one of them said.

In fact, Williams fired no one, even those who had worked hard in Marshall's campaign. He sought out former Marshall employees Robert Bonsib and Robert Harvey Jr. to be deputy state's attorney and chief of criminal trials. And he placed or left other Marshall employees as supervisors of other key units.

Those lingering doubts about staff loyalties came into play in what Williams called "the most difficult case of my 3 1/2 years in office."

It was the case of Gregory Habib. For many of the county's black residents, the incident embodied all of their fears and complaints about a police department historically perceived to be brutal toward the county's black population.

Williams, as had been his policy, investigated Habib's death and presented the findings to a grand jury.

Until the Habib case, said one former assistant state's attorney, Williams deferred to the judgment of his experienced prosecutors. "It appears that he did not rely on their judgment in the Habib case," the former assistant state's attorney said.

Indeed, Williams's screening division -- and others on his staff -- had recommended that the case did not warrant prosecution. But Williams sought charges from the grand jury, which returned only misdemeanor assault charges against one of the officers. And that charge related to the dead man's brother. The charge was later dropped.

Afterward, Williams lambasted the grand jury investigation, some members of his staff and some in the police department for allegedly shaping the investigation.

The county police union, the Fraternal Order of Police Lodge 89, accused Williams of letting politics determine his decisions in the case and demanded an apology. He has not apologized.

"It was clearly a case that had far-reaching political implications," said Darryl Jones, FOP president. "It was not so much what he said but how he said it that annoyed us."

Williams stands by his decisions in the Habib case. "The only thing I regret is that the press focused on the words 'cowboys and renegades,' " he said. "I did not label the whole police department as that, and I know it."