DUBAI, United Arab Emirates — Westerners were getting too racy on the beaches of this Persian Gulf tourist haven, and a police crackdown on topless sunbathing, nudity, and other indecent behavior has resulted in 79 arrests in recent days.

Undercover officers are strolling the sand while others stand guard in new watchtowers to enforce the social mores of this Muslim city-state, which is a booming business center that is attracting growing hordes of foreign tourists.

Authorities said they began the decency campaign after police detained a British man and a woman who were allegedly having sex on one of Dubai’s sprawling beaches earlier this month.

Over the past two weeks, police have detained a total of 79 people whose behavior was “disturbing families enjoying the beach,” a spokesman for Dubai’s Criminal Investigation Department, Zuhair Haroun, said yesterday.

First-time offenders may be issued a warning, but if caught twice, tourists could be referred to the public prosecutor for possible criminal charges, authorities said.

Thousands of European and Asian expatriates live and work in Dubai, where native Emiratis make up only about 20% of the estimated 1.2 million residents. Shopping malls and fast food restaurants have replaced traditional Arab houses, and English has overtaken Arabic as the emirate’s lingua franca.

Many Emiratis and Arabs visiting from other Persian Gulf countries increasingly feel Dubai’s ambition to become a cosmopolitan metropolis and tourist destination is overrunning their own traditions and contradict what they feel is culturally acceptable.

Unlike elsewhere in the conservative Persian Gulf, tourists in Dubai are often seen wearing skimpy bikinis on public beaches and walk the city’s streets in shorts. Alcohol is freely available in hotel bars and restaurants in this regional businesses and entertainment hub.