Factbox-Who are Argentina's presidential candidates?

BUENOS AIRES (Reuters) - Argentines will vote on Oct. 22 to elect a new president, with an ultra-libertarian, a conservative and the ruling coalition's center-left hopeful fighting tooth and nail for the keys to the Casa Rosada government palace amid a spiraling economic crisis.

The new president will take the reins in December, facing down triple-digit inflation, a currency in freefall, and rising poverty.

In an August primary, Javier Milei of the fringe Liberty Advances (LLA) party shattered forecasts by finishing first with 30% support, just ahead of Patricia Bullrich from the center-right opposition alliance Together for Change (JxC) with 28%, and Economy Minister Sergio Massa of the ruling Peronist Union for the Homeland (UP) coalition close behind at 27%.

Polls had predicted that Milei would rank third place or lower. Two other candidates trail far behind: dissident Peronist Juan Schiaretti and leftist Myriam Bregman.

To win outright, a candidate must obtain over 45% of the votes cast, or over 40% together with a margin of more than 10 percentage points over the closest competitor. If no candidate wins outright, the top two finishers will compete in a Nov. 19 run-off.

Here is a summary of the main candidates and their plans:

JAVIER MILEI - LIBERTY ADVANCES

An outsider to Argentina's political establishment, the 52-year-old economist and congressman with tousled hair, fiery speeches and a penchant for rock music was until a few years ago known more as a theatrical TV commentator.

But a devastating economic crisis and disillusionment with those in power helped propel Milei and his harsh anti-establishment message ahead of two experienced heavyweights in the August primaries.

Among other far-right proposals, Milei has vowed to shut down the central bank and dollarize the economy in order to reduce inflation. He also has pledged deep spending cuts alongside plans to privatize health, education and public works in a drastic downsizing of the state.

PATRICIA BULLRICH - TOGETHER FOR CHANGE

A 67-year-old former security minister, Bullrich won the opposition candidacy with an emphasis on restoring "order" and a tough discourse promising to rapidly get rid of capital controls. She has ruled out any negotiations with the Peronists.

Bullrich - who served as minister under the 2015-2019 administration of conservative President Mauricio Macri - beat her JxC rival by a wide margin, but Milei's clear, if narrow, victory among opposition candidates nevertheless marked a stinging defeat.

She argues that cutting government spending is vital to taming inflation and pledged to eliminate taxes as soon as possible on agricultural exports, one of the state's top revenue sources.

SERGIO MASSA - UNION FOR THE HOMELAND

The 51-year-old lawyer and current economy minister is running to maintain the ruling Peronist coalition's hold on the Casa Rosada. His government's leader, outgoing President Alberto Fernandez, will leave office with the economy in crisis.

A former legislative leader and ex-mayor of the Buenos Aires suburb of Tigre, Massa pledges to reduce the government's ballooning budget deficit and strengthen central bank reserves to improve the economy, while betting in traditional Peronist fashion on the domestic market.

Massa adopts a more market-friendly incarnation of Peronism, maintaining contacts with foreign businessmen and Washington, and a shift away from the influential populist leftist movement represented by current Vice President Cristina Fernandez de Kirchner.

JUAN SCHIARETTI - WE DO FOR OUR COUNTRY

The 74-year-old former governor of Cordoba province represents a dissident faction of the ruling Peronist coalition that has split away from Kirchnerism.

He touts his local experience managing public finances, but his party achieved just 3.8% of the vote in the August primaries.

MYRIAM BREGMAN - LEFTIST FRONT

The 51-year-old lawyer represents the country's historical socialist movement through the Leftist Front coalition, which won just 2.7% of the August votes.

(Reporting by Maximilian Heath; Writing by Sarah Morland; Editing by Leslie Adler)