ASHINGTON, June 7 - The battle over a new Congressional map for Colorado, one of the country's most closely watched redistricting cases, ended Monday in a Democratic victory at the Supreme Court. Falling one vote short, the justices refused to hear the Colorado Republicans' appeal of a state high court ruling that invalidated an unusual second redistricting plan the Republicans had pushed through the legislature in the closing days of its 2003 session.

Mid-decade redistricting is part of a national Republican strategy to leverage newly achieved control in a state legislature by redrawing the Congressional map in a way that favors Republicans. A case from Texas is on appeal to the Supreme Court but will probably not be acted on before the current term ends this month.

In invalidating Colorado's new redistricting plan last December, the Colorado Supreme Court said it was relying completely on the state Constitution to conclude that Congressional redistricting could be conducted only once a decade. That decision meant that the district lines reverted to those drawn by a state court in early 2002, after the legislature failed to agree on how to draw new lines following the 2000 census, which gave Colorado a new Seventh District. Under that plan, Colorado Democrats say they have a good chance to pick up two seats.

In November 2002, Republicans gained control of the Colorado legislature. Over Democratic objections, they pushed through a new plan in the final days of the 2003 legislative session.

In drafting an appeal to the United States Supreme Court, the Republicans' challenge - as it had been in Florida after the 2000 presidential election - was to find an issue of federal law to provide jurisdiction. In their appeal, Colorado General Assembly v. Salazar, No. 03-1082, they argued that the federal Constitution's "elections clause," giving state legislatures the power to make rules for Congressional elections, did not allow that power to be transferred to state courts. Consequently, they maintained, the court-ordered plan did not count, and the 2003 legislative plan should prevail.

The appeal evidently provoked a behind-the-scenes struggle among the justices, who considered it at five consecutive weekly conferences before turning it down on what was apparently a vote of 6 to 3, one short of the four necessary to hear a case. The majority offered no comment, and only the dissenters - Chief Justice William H. Rehnquist along with Justices Antonin Scalia and Clarence Thomas - identified themselves.

Chief Justice Rehnquist's opinion, which the other two signed, was reminiscent of his opinion in Bush v. Gore, the Florida case that decided the 2000 election. He said the state court decision, "while purporting" to be based on state law, actually made a "debatable interpretation" of federal law in validating the initial court-ordered redistricting. The decision should be reviewed, he said.