An Alexandria judge rejected a request yesterday from Ronald Reagan supporters that he cancel next Tuesday's Republican presidential preference caucus in the city.

Reagan forces filed suit claiming that the caucus should be canceled because of alleged "election eve fraud" by supporters of George Bush.

But Judge Albert H. Grenadier told attorneys for both candidates yesterday that their dispute is "a party matter" over which he has no control.

Tuesday's Alexandria caucus is a step in the complicated process by which Virginia Republicans will chose delegates to the GOP National Convention in July.

Reagan supporters wanted the city's caucus cancelled because a photocopy of the ballot, mailed to all Alexandria Republicans by Bush supporters, left out a slate of 173 delegates committed to Reagan.

Attorney Leonard B. Sussholz argued that such an omission, whether "intentional or unintentional," would mislead the city's 3,500 Republican voters into thinking that Reagan was not running. That would have the result of keeping Reagan forces away from the polls on Tuesday, and give the election to Bush, he said.

Grenadier said that even if he had jurisdiction in the matter, "I don't see how anyone could be misled by the ballot," which was mailed in a Bush for President envelope and accompanied by a letter saying Reagan had a slate wholly committed to him.

On Tuesday 285 Alexandria delegates will be chosen for two party conventions. The largest slate on the ballot, containing 173 names, is committed to Reagan. Another slate, with 213 names, is labeled uncommitted, although 119 persons on it are openly for Bush. Former Texas Gov. John Connally and Reagan each have a few persons favoring them on the "uncommitted" slate.

Eventually, 51 Virginians will be selected to go to the national convention.

No similar caucus was held four years ago, although city Republicans narrowly supported Reagan over President Gerald R. Ford at regional and state GOP conventions then.