PEORIA, Ill. (AP) _ Key management players in the dispute between striking United Auto Workers and Caterpillar Inc. have something in common with those on the other side: They started out as union workers.

Caterpillar President Jerry Flaherty and Wayne Zimmerman, vice president of employee relations, both joined the company in the 1950s.

Flaherty, 53, began working at Caterpillar's Aurora plant in 1959 and moved into management after earning a master's degree from Northern Illinois University in 1967.

He first sat at the bargaining table in 1988 as vice president of employee relations.

Zimmerman, 56, joined Caterpillar as a machinist apprentice at an East Peoria factory in 1954. He held various manufacturing positions until 1970 when he became production manager at Caterpillar's plant in Glasgow, Scotland.

He became vice president in 1989. These are his first contract negotiations.

Jerry Brust, director of labor relations since 1990, is the most experienced hand on Caterpillar's team.

The 51-year-old started at Caterpillar in 1967 in labor and employee relations.

As point man for Caterpillar's proposal to abandon a contract patterned after a UAW agreement with Deere & Co., Brust has been a lightning rod for union wrath. They have attacked him as ''mean spirited'' and said his white- collar background makes it impossible for him to relate to hourly workers.

He has participated in negotiations six times since 1970, missing only 1979, when a strike lasted 80 days.

The union is represented by two veteran contract negotiators.

UAW secretary-treasurer Bill Casstevens, 63, is chief negotiator for the third time with Caterpillar. He is responsible for contracts that affect more than 125,000 UAW members at Caterpillar, Deere, J.I. Case, Navistar International and others.

He went to work in a cotton mill at age 14, joined the Navy at 16, and later finished high school and earned a business degree from Lynchburg College in Virginia.

He moved to Cleveland and was hired at a Fisher Body plant in 1954.

He was first elected a UAW vice president in 1983 after 13 years as a regional director.

Elliot ''Andy'' Anderson, 49, is Casstevens' top assistant. He is a veteran of four previous Caterpillar negotiations, including the 1979 strike and a record 205-day strike in 1982-83.

He has served as chief aide to three directors of the union's agricultural implement department.

He began his UAW career as a union employee of J.I. Case implement makers in Burlington, Iowa, in 1962; he became local union president there at only 23. He joined the UAW's national staff in 1974.