LOS ANGELES (AP) _ Nine former directors and officers of Gibraltar Savings are named in a $100 million lawsuit by the federal government, which accuses them of steering the Simi Valley thrift into ruin.

The failure of the Gibraltar Financial Corp. unit in 1989 is expected to cost taxpayers $988.6 million, making it one of the most expensive savings and loan collapses. It had heavy losses in mortgage-backed securities, real estate investments and junk bonds.

The Resolution Trust Corp. suit, filed this week in Los Angeles federal court, contends former Chief Executive Herbert J. Young, President Jerome Nussbaum and other defendants were negligent in managing Gibraltar's growth.

The other defendants include Houston I. Flournoy, a former outside director of the S&L who served as state controller from 1967 to 1974.

The lawsuit says Gibraltar failed in 1989 because it paid excessively high interest rates to attract deposits, then aggressively invested in risky securities.

It also accuses Gibraltar officials of ''cherry picking,'' selling high- yield assets to show gains on its financial statements while deferring unrealized losses.

The RTC, which deals with the wreckage of failed thrifts, said in the lawsuit that Gibraltar grew 22 percent a year between 1983 and 1987 but never had ''appropriate internal procedures and controls.''

Officers sued include Young, Nussbaum, Flournoy, James N. Thayer (who served as chief executive after Young), and former Chief Financial Officer John R. Williamson. Also sued were former directors Robert R. Sprauge, Rafael E. Vega, Melvin P. Spitz and Bernice H. Hutter.

Martin Washton, a Los Angeles attorney representing Flournoy and the other former outside directors, said the defendants deny liability for the collapse.

Flournoy, a Republican, ran for governor in 1974, losing to former Gov. Jerry Brown.