Smoky diesel fumes, alleged bias in Japanese hiring, and a Nixon-era newspaper libel suit were among the topics touched by preliminary US Supreme Court decisions Monday. The high court:
- Refused to disturb a ruling that orders automakers to slash diesel engine pollution by 1985.
- Gave the go-ahead for a trial in a libel suit filed against the Washington Post by Charles (Bebe) Rebozo, a close friend of former President Nixon's.
- Agreed to decide whether Japanese-owned companies operating in the United States may practice sex discrimination by hiring only Japanese men for management positions.
- Agreed to decide what school districts must do to supply a ''free appropriate public education'' to handicapped children. The case involves a ruling that a Westchester County, N.Y., school board must provide a sign-language interpreter for an eight-year-old deaf girl.