In his recent sermon, he described the reported massacre of schoolchildren and other Muslim inhabitants in the central city of Meiktila in March, documented by a human rights group, as a show of strength.

“If we are weak,” he said, “our land will become Muslim.”

Buddhism would seem to have a secure place in Myanmar. Nine in 10 people are Buddhist, as are nearly all the top leaders in the business world, the government, the military and the police. Estimates of the Muslim minority range from 4 percent to 8 percent of Myanmar’s roughly 55 million people while the rest are mostly Christian or Hindu.

But Ashin Wirathu, who describes himself as a nationalist, says Buddhism is under siege by Muslims who are having more children than Buddhists and buying up Buddhist-owned land. In part, he is tapping into historical grievances that date from British colonial days when Indians, many of them Muslims, were brought into the country as civil servants and soldiers.

The muscular and nationalist messages he has spread have alarmed Buddhists in other countries.

The Dalai Lama, after the riots in March, said killing in the name of religion was “unthinkable” and urged Myanmar’s Buddhists to contemplate the face of the Buddha for guidance.

Phra Paisal Visalo, a Buddhist scholar and prominent monk in neighboring Thailand, says the notion of “us and them” promoted by Myanmar’s radical monks is anathema to Buddhism. But he lamented that his criticism and that of other leading Buddhists outside the country have had “very little impact.”

“Myanmar monks are quite isolated and have a thin relationship with Buddhists in other parts of the world,” Phra Paisal said. One exception is Sri Lanka, another country historically bedeviled by ethnic strife. Burmese monks have been inspired by the assertive political role played by monks from Sri Lanka’s Sinhalese majority.