Federal Reserve Gov. Martha R. Seger, a consistent advocate for lower interest rates and a generally easier monetary policy in the 6 1/2 years she has been on the Fed's board, announced her resignation yesterday.

Seger said she was leaving in order to earn more money as a "professional corporate board member," teacher and lecturer and to care for her elderly mother, who she said is paralyzed and requires 24-hour care.

In her resignation letter to President Bush, Seger declared, "For nine of the past 10 years -- which should have been my peak earning years -- I have been in public service either in Michigan or in Washington earning subpar wages. Therefore, I must concentrate on increasing my income and replenishing my depleted savings by returning to the private sector."

Seger gave no date for leaving, saying it would take about two months for her to complete a number of projects she has underway.

Her departure gives President Bush an opportunity to make his fourth appointment to the seven-member board. His latest nomination, that of economist Lawrence Lindsey of the White House domestic policy staff, was made this month.

Seger, 58, cited as her major contributions at the Fed "the opening up of securities underwriting to a limited extent at subsidiaries of bank holding companies" and other efforts at liberalizing the activities of bank holding companies.

Since her appointment to a 14-year term by President Reagan in 1984, her role at the central bank has been largely one of an outsider, according to Fed sources.