Republicans pushed back hard Thursday against a request by Sen. Edward M. Kennedy that Massachusetts state election law be changed to empower Gov. Deval Patrick to appoint an interim successor should his Senate seat become vacant.

But state Republican officials have little hope of actually blocking a bill if, as initial signals indicate, Massachusetts Democrats choose to push through an amendment this fall to the state law that leaves the seat vacant until a special election is held.

Republicans tried to strike a respectful tone, even as they called Kennedy's request, made in a letter to Patrick and leaders of the Massachusetts state House and Senate sent this week, essentially a political ploy.

"We must honor Sen. Kennedy's service by allowing those who sent...