NEW YORK (Reuters) - Outside the crumbling Brooklyn building where the first U.S. birth control clinic opened 100 years ago, Alexander Sanger reflected on the move that landed his grandmother in jail and fueled a controversy over women's reproductive rights that has raged ever since.

"This is where it all started," said the grandson of Planned Parenthood founder Margaret Sanger in his first visit to the Brownsville, Brooklyn, site where she started her clinic in 1916.

"She threw down the gauntlet and said, 'Preventing women from contraception is inhumane,'" said Sanger, 68, chairman of the International Planned Parenthood Council and a former president of Planned Parenthood New York City.

City records show the desolate building with bricked up windows is not abandoned, although it appears unoccupied, a far cry from the busy clinic shown in historic photographs with baby carriages parked out front.

Some of the reproductive rights battles that Margaret Sanger fought a century ago were remarkably similar to the challenges facing Planned Parenthood today, particularly organized religion's objection to sex education, her grandson said.

"There is a direct correlation," he said. "If the hormones are raging among young people and you don't get them preventive information and preventive methods, they are going to get pregnant."

Father Frank Pavone, national director of Priests for Life, said the Roman Catholic Church's opposition was rooted in a far deeper philosophical divide.

"It's not just a question of 'Let's teach them sex education so they'll know how to prevent the pregnancy,'" Pavone said. "The fundamental disagreement comes on that basic question of 'What's human sexuality all about?'"

The religious-liberty fight over contraception is back in the U.S. Supreme Court, which will rule by July on whether religious groups deserve a blanket exemption so that they do not have to pay for their employees' contraceptive coverage as mandated under President Barack Obama's Affordable Care Act.

Abortion is the flashpoint in other conflicts that are vastly and violently different from those Sanger faced before her death in 1966.

Opponents have waged a decades-long string of attacks on abortion providers, the most recent in November when a gunman killed three people at a Colorado Springs Planned Parenthood clinic. Since 1993, there have been 11 murders and 26 attempted murders due to anti-abortion violence, according to the National Abortion Federation, a group of healthcare providers.

Lawmakers continue to tighten restrictions on abortion, with 288 such limits passed by states since 2011, according to Elizabeth Nash of the Guttmacher Institute, a non-profit that focuses on reproductive health.

The Supreme Court also plans to rule on a Texas law that mandates costly hospital-grade facilities for abortion providers, who say it actually aims to shut clinics and chip away at a woman's right to terminate a pregnancy.

Planned Parenthood itself is in the crosshairs, with the Republican-led Congress voting as recently as this week to cut all of its federal funding, although Obama, a Democrat, has vowed to veto the measure when it reaches his desk.

A USA Today poll in December found Americans overwhelmingly oppose cutting off federal funds for Planned Parenthood. Some 59 percent of Republicans and 89 percent of Democrats are against the idea.

DEMANDING ACCESS

The controversy was well under way 100 years ago when Sanger and her sister, both trained nurses whose mother died young after giving birth to 11 children, opened the clinic. They fitted women for diaphragms, which were the most effective birth control available at the time but were illegal under the federal Comstock Law against distributing materials that could be used for contraception.

"The women were lined up and demanding access to birth control," her grandson said. "That said it all."

One patient turned out to be an undercover police officer, and nine days after the clinic opened in the low-income Jewish and Italian neighborhood, it was shut down, and Sanger was under arrest.

Margaret Sanger's holy grail was universal access to birth control for women, whose unplanned pregnancies forced them into what she viewed as sexual servitude.

Sanger, who founded organizations that evolved into Planned Parenthood Federation of America, was a driving force in the early 1950s behind the development of the birth control pill, which today is largely credited with allowing women to shape their lives and compete in the workplace with men.

"Birth control has been central not just to women's political, workplace and education opportunities but also to their ability to live," said Carrie Baker, who teaches women's studies at Smith College in Northampton, Massachusetts. "What motivated Margaret Sanger was that women were dying after having so many pregnancies."

Today about half of the 6.6 million pregnancies annually in the United States are unintended, a higher proportion than in Europe, reproductive health experts say.

Teen birth rates in Brownsville, now a mostly black neighborhood that is one of the city's poorest, are among the highest in New York City, and the abortion rate is double the rest of the city, according to the city health department.

"It's still the poorest of the poor who are having more children than they want, who are having children earlier than other women, who are not getting access to preventive methods when they need them - whether it's in Brownsville or Rio de Janeiro," Sanger said. "That same struggle was my grandmother's struggle, and it is mine."

(Reporting by Barbara Goldberg; Editing by Lisa Von Ahn)