Dissident Teamsters said yesterday they have abandoned efforts to overturn the union's new three-year contract with the trucking industry.

They said the decision came after the union's leaders agreed that in future contract-ratification votes the ballots of part-time truckers, known as casuals, would be counted if they work at least 80 days a year.

The agreement was announced in U.S. District Court here yesterday.

In the past only members with full-time jobs or laid-off members with recall rights were allowed to vote. The dissidents said this discriminated against part-timers, whose base pay was cut by the new contract from $13.21 an hour to $11. The agreement, which raises full-timers' hourly pay by $1.50 over three years, also discourages widespread hiring of casuals.

The contract went into effect May 17, immediately after being ratified by a membership vote of 62,296 to 54,873. A few hours after ratification was announced, lawyers for the dissidents told U.S. District Judge Charles R. Richey that about 35,000 part-timers had not been able to vote. However, a court-ordered survey of union locals found only 2,933 casuals who had not been sent ballots.

Yesterday Ken Paff, national organizer for the dissident Teamsters for a Democratic Union, based in Detroit, said, "We were unable to prove our number so we were unable to win that issue in court."

Alan B. Morrison of the Public Citizen Litigation Group, which represented the dissidents, called the settlement a "fair compromise."

Teamster attorney Joseph E. Santucci Jr. said the settlement will avoid "disproportionate" influence by casuals having "only intermittent contacts with the industry."