ATHENS, Greece — Earlier this year on an Arabic Web site, a Muslim woman scholar posted an open letter to the Islamic world. "Take off the veil, sister," began Elham Manea, a professor of Yemeni descent who now works in Switzerland.

Her opinion was not new — that head scarves and other coverings for women are not mandated by the Quran or Islamic tradition. But the essay's impassioned tone quickly grabbed attention. Supporters hailed it as a timely manifesto against Islam's conservative tide. Traditionalists scorned it as the ramblings of a Muslim blinded by the West.

Both sides could agree, however, that despite all its cultural twists, the question of the veil is a religious one, and one that's stubbornly hard to pin down — just what does Islam demand?

With no central Islamic theological authority — such as the Vatican for Roman Catholics — Muslims are left to interpret Quranic passages, sift through stories about the Prophet Muhammad, known as hadiths, and study competing religious edicts over the various coverings. They range from fashionable head scarves to the shroud-like burqa and the full-face veil called a niqab, which may only show a woman's eyes.

"It's become such a charged topic," said Manea, a researcher on politics and Islam at the University of Zurich. "I received hate mail and e-mails with very threatening tones. But, on the other side, messages supporting my views also were overwhelming."

In the West — particularly Europe — the veil has been drawn into debates on immigrant integration and worries about radical Islam.

Here in Hawai'i, veils have been discussed at length. While you'll see veils on most Muslim women at public events celebrating Islam, such as Eid al-Fitr, the festival that ended Ramadan last month, several Muslim women admit they take a more liberal approach in public and don't wear veils at work or while shopping.

And inside the Honolulu mosque, there have been other pressures to treat women as men: In 2005, gender segregation in the Muslim Association of Hawai'i was a hot topic in which some urged that women be allowed to pray as a group behind men in the main prayer hall, rather than be physically isolated by curtains, walls or separate rooms as they are in the majority of U.S. mosques.

In other cities, some are also calling for greater shared leadership, with more women serving on governing boards and as public speakers at community programs.

In many Muslim countries, it can represent a potentially life-shaping decision for women in which the veil is increasingly seen as a political statement against perceived injustices to Islam.

"There are so many pressures now to decide whether the veil is right or wrong," said Tarafa Baghajati, a leader of the European Network Against Racism in Brussels, Belgium. "The problem is that it's an impossible task."

Credible cases have been built in several directions.

Those supporting the veil often cite a hadith from Sahih Bukhari, 9th-century theologian, that urges women to "cover themselves" in public. The Quran, too, contains sections that tell women to seek modesty and "draw their cloaks close around them" (Surah 33, verse 59) and "draw their veils" over their chests and necklines except around their husbands and close relatives (24:31).

Some prominent Islamic voices, including Egyptian-born cleric Sheik Yusef el-Qaradawi, say some form of Islamic coverings is supported by Muslim law and customs. But most don't go beyond advocating some variation of head scarves and body-covering clothing.

Far fewer leaders — outside ultraconservative bastions such as Saudi Arabia and Afghanistan — believe Islam requires veiling a woman's face and hands, saying that both are exposed during prayer and that a woman's face should not be covered during the Hajj, or pilgrimage, to Mecca.

But many other Islamic scholars find flaws in any demands for the veil, which is often called by the Arabic term "hijab."

They believe the phrasing in the Islamic texts is too vague to make it a religious requirement — in the same way that the Bible and Jewish sources offer guidance that is now widely considered a matter of personal choice, such as a passage in I Corinthians that says a woman should cover her head during prayer.

"The hijab these days goes beyond religion into politics, culture and social," said Ahmed Nazeer, American Institute of Islamic History and Culture in Concord, Calif. "These pressures are all coming down on Muslim women — to make a statement in favor of the one vision of Islam or another."

Last week, a Turkish court acquitted a 92-year-old archaeologist, Muazzez Ilmiye Cig, who was charged with insulting religious feelings in her book that claimed Islamic-style head scarves were first worn more than 5,000 years ago by priestesses initiating young men into sex.

Turkey offers a vivid display of the modern interplay of politics and shifting religious sensibilities.

Turkey's strongly secular laws ban head scarves in schools and public offices. But growing ranks of Turkish women favor head scarves in daily life — a trend echoed in some Muslim immigrant groups in Europe and elsewhere.

"There is powerful symbolism associated with the veil in the West," said Dogu Ergil, a professor of social and religious trends at Ankara University in Turkey.

"It feeds into the insecurities of our globalized world: the threats to the way we look, the way we live and the fears about the stranger in our midst who may be hostile to our way of life."

Tariq Ramadan, a leading scholar on European Islam, told a London conference last week the veil was part of a deepening "them versus us" attitude.

The 1979 Islamic Revolution imposed strict dress codes that allowed either a head scarf and formless coat or the billowing black chador, which covers all but a woman's face. Since the late 1990s, it's possible to get by with a body-hugging tunic and a scarf that can reveal more hair than it covers.

Iranian religious authorities realize any edict re-enforcing stricter hijab would be likely countered by liberals acknowledging the desires of the young.

Instead, the theocracy has tried a stab at vanity — backing a fashion show in July that displayed their concepts of chic-but-conservative coats, head scarves and chadors.

Advertiser religion & ethics writer Mary Kaye Ritz contributed Hawai'i information to this report.