GRAND RAPIDS, Mich. (AP) _ A circuit judge on Thursday overturned a change in state Republican Party rules, which was aimed at curtailing Vice President George Bush's campaign effort in Michigan.

The state will select the nation's first GOP presidential delegates later this month.

The decision by Kent County Circuit Judge Roman Snow was the second legal victory for Bush supporters against a coalition of Pat Robertson and Jack Kemp supporters that controls the state party.

Bush supporters said the triumph was the biggest yet in their bitter battle with the Kemp-Robertson coalition.

''Magnificent. It's a big, big win,'' said Peter Secchia, one of four Bush co-chairs in Michigan and a member of the Republican National Committee.

''It was a pretty ringing decision by the judge,'' said John Long, the director of Bush's Michigan campaign. ''He was very firm in his decision that it (the rule change) was untimely and unlawful.''

Leaders of the Kemp and Robertson efforts in Michigan pointed out that several legal avenues remain.

''Our feeling is that this whole matter has yet to be exhausted through the courts,'' said Paul Welday, deputy director of Kemp's Michigan effort.

Said Lori Packer, director of Robertson's Michigan campaign, ''I still feel that we're right and we're going to keep fighting.''

Snow ruled that a Dec. 12 rules change by the 101-member Republican State Committee - controlled by the Robertson-Kemp coalition - violated national party rules and state law. And Snow said the changes also violated another Kent County Circuit Court judge's ruling.

After a shaky start, Bush forces mounted a strong effort in Michigan and diluted Robertson's surprising showing by prevailing at the county level on apportionment and redistricting decisions for delegates to the county conventions.

About 10,000 Republicans will attend next Thursday's county conventions and choose about 1,800 delegates to the Jan. 29-30 state convention, where Michigan's presidential delegates will be parceled out, more than a week before the Iowa caucuses.

''It is clear the county committees have been given the authority (under state law) to select the system for selecting delegates,'' Snow said, echoing a Dec. 4 ruling by Judge George V. Boucher that struck down Sept. 15 rules changes sought by the Kemp-Robertson coalition.

Michael Gagleard, the attorney for the state party, argued that it was an internal GOP question and didn't belong in the courts.

''The heart of the matter ... is an intra-party fight in the Michigan Republican Party,'' he said.

Michael Legg, a state committee member who was appointed to oversee the legal action, said the committee now would focus its attention on its appeal of Boucher's ruling and a lawsuit pending in U.S. District Court in Detroit.

A handful of Robertson and Kemp activists filed the lawsuit on Dec. 15, seeking to have the state laws behind Boucher's decision declared unconstitutional. A hearing on the federal lawsuit has been scheduled for Tuesday.

Legg, one of the leaders of Kemp's Michigan campaign, acknowledged that if no other court decisions are made to supersede Snow's decision ''the state committee would abide by it.''