WASHINGTON — Since his first homily in 2013, Pope Francis has preached about the need to protect the earth and all of creation as part of a broad message on the environment. It has caused little controversy so far.

But now, as Francis prepares to deliver what is likely to be a highly influential encyclical this summer on environmental degradation and the effects of human-caused climate change on the poor, he is alarming some conservatives in the United States who are loath to see the Catholic Church reposition itself as a mighty voice in a cause they do not believe in.

As part of the effort for the encyclical, top Vatican officials will hold a summit meeting Tuesday to build momentum for a campaign by Francis to urge world leaders to enact a sweeping United Nations climate change accord in Paris in December. The accord would for the first time commit every nation to enact tough new laws to cut the emissions that cause global warming.

The Vatican summit meeting will focus on the links between poverty, economic development and climate change, with speeches and panel discussions by climate scientists and religious leaders, and economists like Jeffrey Sachs of Columbia. The United Nations secretary general, Ban Ki-moon, who is leading efforts to forge the Paris accord, will deliver the opening address.