The

White House

Monday made

Securities and Exchange Commissioner

Laura Unger acting chairwoman of the agency, filling its top post while President Bush seeks a permanent replacement for just-retired SEC Chairman Arthur Levitt.

The interim appointment had been

expected since Bush prevailed in last year's protracted presidential contest. Unger is the sole Republican on the regulatory commission.

Levitt, who retired from the commission on Friday, was its longest-serving chairman. He was appointed by President Clinton in 1993. Clinton had similarly appointed an interim SEC chairwoman, Mary Schapiro, to lead the agency while Levitt awaited

Senate

confirmation.

Unger became a member of the commission in November 1997. As a commissioner, she has taken the lead in exploring implications of electronic trading in the securities markets, and completed a

report on online brokerages in late 1999.

Unger could not be reached for comment on the interim appointment Monday.

Before serving with the SEC, Unger had been a securities counsel to the

Senate Banking Committee

in Washington and a staff lawyer for the SEC's enforcement division.