[3] After defeating incumbent Joseph Scancarella in 1971, Klein served as a member of the New Jersey General Assembly from 1972 to 1976.

In the Assembly, was co-counsel on a bond issue for New Jersey Sports and Exposition Authority, and worked for the introduction of state income tax.

He co-authored the bills that authorized interstate branch banking and was the architect of the provision which sparked passage of the legislation that ended the problems in the savings and loan industry.

[3] Klein also served on the House Science Committee, where he co-authored the National Competitiveness Act which helped to strengthen American industry.

Klein was defeated for re-election by Clifton city councilman and Passaic County freeholder Bill Martini, making him one of 54 Democrats to lose their seats in the 1994 Congressional Elections.