D.C. Mayor Marion Barry announced yesterday he has nominated Marianne Coleman Niles, a lawyer with the Consumers United Insurance Co., to become the city's director of the Office of Campaign Finance.

Niles, who is serving as acting director pending confirmation by the D.C. Council, would succeed Keith A. Vance, who served as director for nearly five years and withdrew his name from consideration for renomination this month. Vance will become the chief of administration for the District's Department of Human Services, according to a Barry spokesman.

The director of the Office of Campaign Finance, which oversees the city's ethics and campaign spending laws, is responsible for monitoring politically sensitive details of campaign reporting. When Vance's term expired in March, Barry aides said the mayor wanted to appoint a lawyer to the position. Vance, a former federal elections official who was paid $69,556 a year, is not a lawyer.

Niles, 42, is a graduate of Georgetown University Law Center and Howard University. Before serving as general counsel for Consumers United, Niles worked for the District government for 15 years, holding a variety of jobs, including program manager for the mayor's Office of Policy and Program Evaluation from 1985 to 1986.

"Mrs. Niles brings a wealth of experience to her new position and I am sure she will do an outstanding job," Barry said through a spokesman. "She is qualified by both her legal training and prior career experience, outside and inside the government, to manage this important and sensitive agency."

Niles said, "I am extremely pleased to have been selected for this key position."

During his tenure as campaign finance director, Vance was credited with making substantial improvements in processing and filing thousands of campaign records and financial disclosure forms.

But Vance's critics said he was too close to Barry, following decisions to take no action regarding numerous allegations of violations of reporting requirements by members of the Barry administration.

Vance conducted a lengthy investigation of the campaign finances of D.C. Council member Charlene Drew Jarvis (D-Ward 4) following allegations of reporting violations in her 1982 mayoral and 1984 council campaigns. Some political observers believe the investigation may have cost Vance support on the council.

As a result of Vance's investigation, Jarvis paid a $10,000 fine to settle complaints about reporting violations.