WASHINGTON, Oct 29 (Reuters) - Kamala Harris' lead over Donald Trump dwindled in the final stretch of the U.S. presidential contest, with the Democrat ahead by a single percentage point over the Republican, 44% to 43%, according to a Reuters/Ipsos poll published on Tuesday.

The three-day poll, completed on Sunday, showed the race effectively tied ahead of the Nov. 5 election. The poll had a margin of error of about three percentage points in either direction.

While Harris has led Trump in every Reuters/Ipsos poll of registered voters since she entered the race in July, her lead has steadily shrunk since late September. A prior Reuters/Ipsos poll conducted Oct. 16-21 showed Harris, the current U.S. vice president, with a two-point lead over former President Trump.

The new poll, which surveyed 1,150 U.S. adults nationwide, including 975 registered voters, showed Trump with significant advantages over Harris on several of the issues voters consider most pressing.

Asked which of the two candidates had a better approach to the economy, unemployment and jobs, voters in the poll picked Trump 47% to 37%. Trump has had an edge on the economy throughout the campaign and 26% of voters in the latest poll cited jobs and the economy as the country's most pressing problem, compared to 24% who cited political extremism and 18% who pointed to immigration.

Trump's biggest edge in terms of policy could be on immigration issues, where he has put forward hardline proposals that include mass deportations of migrants in the country illegally. Some 48% of voters in the latest poll said Trump's approach to immigration was best, higher than the 33% who picked Harris.

The poll also showed Harris' advantage on the issue of political extremism to be dwindling. Some 40% of voters in the poll said she had a better approach to handling political extremism and threats to democracy, compared to 38% who picked Trump. Harris' two-point lead on the issue compared to her seven-point lead over Trump on extremism the Oct 16-21 poll.

Harris has emphasized Trump's role in the Jan 6, 2021 assault on the U.S. Capitol by his supporters, who aimed to overturn his 2020 election defeat, and on Tuesday is making what her campaign billed as her last major pre-election speech before the election at the site where Trump rallied his supporters before the riot.

Trump has hit back with an argument that Harris' views are extreme and would amount to a socialist takeover of U.S. institutions.

Harris' marginal lead over Trump might not be enough to win the election even if it holds through Nov 5.

National surveys, including Reuters/Ipsos polls, give important signals on the views of the electorate, but the state-by-state results of the Electoral College determine the winner, with seven battleground states likely to be decisive.

Trump defeated Democrat Hillary Clinton in the 2016 election, triumphing in the Electoral College even though she won the national popular vote by two points.

Polls have shown Harris and Trump are neck and neck in those battleground states as well.

Given the close match, the candidates' efforts to ensure that their supporters actually cast ballots will likely be key in determining the winner.

Just two-thirds of U.S. adults voted in the 2020 election, which was the highest turnout in over a century, according to estimates by the U.S. Census Bureau and the Pew Research Center.

Some 89% of registered Democrats and 93% of registered Republicans in the poll said they were completely certain they would vote. That points to potentially more enthusiasm over voting now compared to four years ago, when a Reuters/Ipsos poll in late October of 2020 showed 74% of Democrats and 79% of Republicans said they were certain to cast ballots.

Among the respondents in the latest poll who appeared most likely to vote, Harris also had a one-point lead over Trump, 47% to 46%.

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Reporting by Jason Lange; Editing by Scott Malone and Alistair Bell