It's the furthest a District of Columbia voting rights bill has made it since 1978, but whether it will make it any further is far from assured.

The Senate is poised on Tuesday to cast votes on a bill that would add two seats to the House: one in the Democrat-heavy District, and one in Republican-heavy Utah. The bill already has passed the House. If signed into law, it would give the District its first-ever full voting member of Congress.

Tuesday's vote would be a procedural tally on cloture for the measure. A "yea" vote would mean that the Senate won't filibuster the bill and agrees to move on to final passage of the bill.

But cloture is by no means assured, and President Bush has threatened to veto the bill. Bush and the Senate's top Republican, Mitch McConnell of Kentucky, both say the proposal is unconstitutional. Both Republicans and Democrats are fighting for a handful of centrist votes to win the upper hand.

Right now, the District is represented in the House by a non-voting congressional delegate, Eleanor Holmes Norton. The Senate has no counterpart. (Four congressional delegates as well as one resident commissioner from Puerto Rico are elected to the House. The two classifications have the same powers, according to the House clerk's office, though delegates serve two-year terms and the resident commissioner serves a four-year term.)

Delegates can vote on committees and participate in House debate but cannot vote on final legislation.

The bill's supporters are framing the it as a civil rights issue, saying a filibuster would violate decorum.

"Not since segregation has the Senate blocked a voting rights bill, and this is a voting rights bill," D.C. Mayor Adrian M. Fenty said Monday, speaking to reporters outside the Senate.

Former Rep. Jack Kemp of New York joined Fenty and called on senators to support the measure

"Vote your conscience. Vote the American way. Get on the right side of history," Kemp said.

McConnell on Monday took time on the Senate floor to speak out against the bill, saying he's not seeking to deny residents the right to vote.

"My opposition to this bill rests instead on a single all-important fact: It is clearly and unambiguously unconstitutional. It contravenes what the framers wrote, what they intended, what the courts have always held, and the way Congress has always acted in the past," McConnell said.

"And to vote for it would violate our oath of office, in which we solemnly swear to support and defend the Constitution. If the residents of the District are to get a member for themselves, they have a remedy: amend the Constitution. But the members of this body derive their authority from the Constitution. We are its servants and guardians. And we have no authority to change it on our own," he said.

McConnell also pointed to the Constitution's Article I, Section 8 language — 220 years old as of Monday — that allowed Congress to create the District of Columbia.

The paragraph establishing the District reads: "The Congress shall have the power ... to exercise exclusive legislation in all cases whatsoever, over such District (not exceeding 10 miles square) as may, by cession of particular states, and the acceptance of Congress, become the seat of the government of the United States ... .

"The framers clearly envisioned the federal city as a separate entity from the states, as an entity they themselves would control," McConnell said.

Sen. John Warner of Virginia is one of the key Republicans the bill's proponents were hoping would support cloture, but he has said he would rather oppose cloture and introduce a constitutional amendment that would make the District a state.

"Only a constitutional amendment . . . will resolve this issue, and thereby avoid interminable litigation flowing from an Act of Congress," Warner said, according to The Washington Post.

Utah, added to the measure earlier this year to gain support for the bill, was only 857 people shy of gaining its fourth House seat in 2000 by population. Officials have argued that the government should have counted more than 11,000 Mormon missionaries living overseas.

The Associated Press contributed to this report.