Black Protestants were by far the most likely religious group to hear political endorsements from members of their clergy. Black churches have long served as mobilization centers for political candidates and social causes, and this year appears to be no different. Nearly three in 10 black Protestants said they had heard members of their clergy support or oppose candidates in church compared with one in 10 churchgoers over all. And in black churches, Mrs. Clinton was usually the beneficiary.

The survey was conducted before both the Republican and Democratic National Conventions.

Though candidate endorsements were relatively rare, clergy members spoke frequently about social and political issues, the survey found. About two-thirds of recent churchgoers said they had heard clergy members speak about — in order of frequency — religious liberty, abortion, homosexuality, immigration, environmental issues or economic inequality. The first three issues are favorite themes for conservative clergy members, both Protestant and Catholic.

Scant talk about candidates in churches is not surprising. An amendment to the tax code passed by Congress in 1954 prohibits clergy members in churches from endorsing or opposing political candidates, though there is no prohibition on discussing political issues. The Johnson Amendment — named after its sponsor, Lyndon B. Johnson, then a senator — applies to all charitable organizations that accept 501(c) tax-deductible contributions, which includes churches and other houses of worship. Those that violate the law could have their tax-exempt status revoked by the Internal Revenue Service, but it has rarely happened.