Colorado voters have delivered the state for the Republican presidential candidate in every election in the last half century, except when Bill Clinton won by a whisker in 1992 and Lyndon B. Johnson swamped Barry Goldwater in 1964.

But if a ballot initiative called Amendment 36 is approved by the voters here on Election Day, the facade of unanimity will shatter, and in one stroke a new small state's worth of definitively Democratic Electoral College votes will be created in the heart of what has been the solidly Republican West.

Amendment 36 would make Colorado the first state to distribute its electoral votes on the basis of its popular vote. The change would take effect immediately with this year's election, which means that President Bush and Senator John Kerry would share Colorado's nine electoral votes, but neither would get all.

Political experts say the implications for the election are deeply uncertain. A Rocky Mountain News/News 4 poll released Friday showed Mr. Bush and Mr. Kerry in a statistical dead heat here.

Mr. Bush received just under 51 percent here in 2000, which, under the proposal, would be good for five of the nine votes.

If Amendment 36 passed it would essentially create a ministate within a state. For example, if a majority of voters go for Mr. Bush, Mr. Kerry could still collect four electoral votes. That is the total electoral allotment for New Hampshire.

"It could set a dramatic and amazing precedent," said James G. Gimpel, a professor of government at the University of Maryland. "When one state pursues a particular new initiative or new idea, other states tend to take a look."

Republicans have led the effort to defeat the measure. But political analysts say that sentiment could shift if Mr. Kerry appeared more likely to win here.

Supporters landed the measure on the ballot after collecting 134,000 signatures with help from a foundation in Phoenix that wants the Electoral College system scrapped nationwide. The amendment's backers say that voters are ready to try something new and that simply mentioning the 2000 election was enough to induce many people to sign.

"A lot of times, all you had to do was say the word Florida," said Rick Ritter, a Democratic political consultant who helped organize the petition drive. Mr. Bush won Florida's 25 electoral votes, tipping the balance for his victory in 2000, even though he lost the popular vote nationally to Vice President Al Gore.

Although two states, Nebraska and Maine, allow each Congressional district's voters to determine that district's electoral vote, neither state has ever split its votes as a result. Colorado's system would guarantee a split every time.

Opponents of the measure say that a proportional distribution would make Colorado even less relevant than it is now in presidential elections, since the difference between winning and losing might just be one electoral vote. Supporters say the state would matter as never before.

The backdrop for the issue is the ever-increasing polarization of the nation, a fact that many political experts say is exaggerated by the Electoral College, with its winner-take-all mechanism. The candidates this year are not competing at all in a majority of states -- some large, like California; others small, like Idaho -- because they think they cannot win there or they cannot lose there.

Colorado's proposal would make those calculations -- who benefits, who competes, who is wooed -- intensely local, down to individual voters like Joyce Fischer, a retired speech therapist and Democrat.

"I have very mixed feelings about this issue of dividing electoral ballots," Mrs. Fischer said between answering telephones as a campaign volunteer for Ken Salazar, the Colorado attorney general and a Democratic candidate for the United States Senate. "Originally, I thought, gee, this sounds like it's not a bad idea. But speaking as a Democrat, if Kerry does win in Colorado -- or when he wins -- he should have all of the electoral votes."

When it comes to Amendment 36, Mrs. Fischer added, "I'm not 100 percent sure how I'm voting."

Some Republicans are less ambivalent.

"It stinks," said Rick Murray, a financial broker in Highlands Ranch, who was picking up tickets for a rally for Mr. Bush in Colorado this week.

"Right now, the Democrats are just trying to pick up a few electoral votes for Kerry during a close election," Mr. Murray said. "Why don't they try this out in California or New York or Oregon, someplace that typically votes Democrat, instead of picking a Republican state? I think the idea stinks unless it's universal."

Other opponents of the measure say the change could make Colorado a political backwater; or worse, a laughingstock.

"The debate over the Electoral College has gone on for some time, and it's a debate we need to have, but this isn't about that," said Katy Atkinson, director of an opposition group called Coloradans Against a Really Stupid Idea. "This is whether Colorado is going to be the lone state to try an untested system that could put us at a disadvantage."

The winner-take-all system, historians say, was a deeply partisan creation from the beginning, in the late 1700's, when the Federalists saw it as a means to retain power. It did not work out as they had hoped -- they were last elected to national office in 1796 -- but the system stuck.

Many political strategy experts say the politics of one state with a system like the one envisioned in Amendment 36 would be dizzying.

Professor Gimpel, who co-wrote "Patchwork Nation," a book about the geography of voting patterns that includes a chapter on Colorado, said he thought that future presidential candidates would focus on just eight counties with strong Democratic or Republican majorities and ignore the rest. All eight are in and around the so-called Front Range, extending north and south from Denver, where the population is concentrated.

Another academic who has studied geographic voting patterns said he thought presidential campaigns would simply take for granted those existing areas of strength in Colorado and might not bother to campaign at all, especially if the payoff was only a single electoral vote.