By Sarah Morland

SANTIAGO (Reuters) -Chile's gradual expansion of abortion access is at risk of a dramatic reversal as far-right candidate Jose Antonio Kast, a staunch Catholic who opposes even morning-after contraception, surges toward a likely presidential runoff victory in December.

Abortion in Chile, which was completely banned under the 1973-1990 military dictatorship of General Augusto Pinochet, was partially decriminalized in 2017, when it became legal only in cases of risk to the woman's life, fetal inviability and rape.

Kast has sought not only to block a proposed loosening of abortion restrictions backed by the outgoing leftist Boric administration, but also to roll back the existing exceptions to the ban. Those moves would mark the country's sharpest retreat on reproductive rights in decades.

Kast, a father of nine, is a coalition ally of Johannes Kaiser, a Chilean Orthodox Christian who has also pushed to revisit allowing abortion after rape.

Support for the Kast and Kaiser's far-right coalition, fueled by anxiety over crime and migration, surged in Chile's November general elections, boosting its influence in the legislature. Polls, however, show public opinion overwhelmingly supports maintaining existing abortion rights.

"There is an imminent threat to the reproductive rights of girls and women in Chile, putting at risk access to contraceptives, the morning-after pill, and abortion by three exceptions, and blocking any legislative progress to expand these guarantees," said Catalina Calderon, an advocacy director at a regional rights group, the Women's Equality Center.

Broad support from other right-wing blocs is expected to win Kast an easy margin in the December 14 presidential runoff, when he will run against government-backed leftist Jeannette Jara, who was the top vote-getter in the first round vote.

Jara initially said she would ensure abortion is legalized for everyone up to 14 weeks of pregnancy, but later backtracked and said only that she would promote a debate to discuss this legalization, in the face of opposition from Christian coalition allies.

Abigail Mariqueo, 21, a kindergarten teacher living in Santiago, told Reuters she believed a Kast presidency might repeal existing reproductive rights but confronting insecurity was more important. "I feel like it could happen," she said, adding she supported existing rights. "But right now, security has got to be the priority."

Insurance saleswoman Anahi Salazar, 52, said more was needed to fight teen pregnancy. "My family is all very religious," she said. "But people need to be able to choose."

KAST SAYS HE SUPPORTS LIFE FROM CONCEPTION TO NATURAL DEATH

Should Chile reverse abortion rights, it would join a series of governments cracking down on access to the procedure in Latin America, where only a handful of countries permit abortion.

Access remains hampered by funding and social backlash, and is restricted to a set time limit after becoming pregnant - often around three months.

While Mexico's Supreme Court ruled criminalizing abortion unconstitutional in 2021 and its states have gradually been amending their laws, in October Costa Rica limited abortion to women whose life is at risk.

Argentina in 2020 became the first major country in Latin America to legalize abortion up to 14 weeks, but even there, spending cuts under anti-abortion President Javier Milei have led to shortages in key abortion pills and services.

While prison sentences for abortion are rare in Chile, activists say criminalization pushes women into clandestine procedures and a flourishing black market economy that profits off sales of unregulated medications and risky procedures.

Kast has focused on security issues, but when pushed during Chile's last presidential debate about his views on abortion, he said he has not changed his position from prior campaigns, when he opposed pharmacies selling the morning-after pill and called for a repeal of the three existing grounds for legal abortion.

"I support life from conception to natural death," said Kast, who has called himself a Catholic first and politician second.

Kast's campaign team did not respond to requests for more information on his policies.

STATE COULD USE BUDGET CUTS TO RESTRICT ABORTION

Claudia Sarmiento, a constitutional law expert at Chile's Alberto Hurtado University and a former government advisor, said even if Kast doesn't choose to pick a fight over abortion, he and his coalition could try to go after reproductive rights through cuts to state-funded medical and contraceptive programs.

"What's most important, whether or not the law is changed, is the budget," she said, noting that access to contraception is governed by the budget law, controlled by the executive.

New cuts to services ensuring access to contraception and abortion could come amid a broader austerity program, she said, but "disguise a very specific intention regarding women's sexual and reproductive rights."

Even under leftist rule, however, activists said not enough was done to ensure access to legal terminations.

A source who works for With Friends and At Home, a network that helps Chilean women access abortions, said many women she worked with avoided the state system for fear of legal trouble or social backlash.

The source, who spoke on condition of anonymity for security reasons, said around a third of women and girls who seek support from the network have legal grounds for abortion, but many are wrongly turned away or misinformed in hospitals. She estimated some 10,000 come to the network for help each year.

This suggests the vast majority of Chilean abortions are carried out clandestinely or abroad. Chile's health ministry logged just over 6,600 abortions since the former blanket ban was eased in late 2017 - with rape the least-cited reason. For young girls aged under 14, rape represented more than 99%.

The source said further restrictions, such as restricting sales of the commonly used morning-after pill - which could prevent women and girls obtaining it within the hours-long window during which it is effective - and asking women to file criminal charges if seeking abortion after rape, would push more women towards illegal abortions.

"We all know how the judicial system re-victimizes women in relation to sexual crimes," she said. "Many women are victims of sexual violence from family members or intimate partners, so forcing them to file charges brings up a lot of fear."

(Reporting by Sarah Morland and Nicolas Cortes in Santiago; Editing by Claudia Parsons)