The letter comes after Donald Trump announced plans to cut the budget for international aid and diplomacy by 28 per cent, leaving around £20.6 billion.
He has already announced an increase of £43 billion for defence spending, raising it to £515 billion.
Signatories of the letter calling for a u-turn include the Christian charity World Vision, the rock band Third Day, singer-songwriters Matt Maher and Amy Grant, the National Evangelical Association, Southern Baptist Convention and Caridnal Timothy Dolan, the Archbishop of New York.
The letter's addressed to President Trump as well as his Vice-President Mike Pence, Secretary of State Rex Tillerson, as well as Democratic politicians.
It says: "As Christian leaders, it's an honor to represent dedicated and faithful citizens living in every congressional district in this country.
"Today, there are 65 million displaced people, the most since World War II, and 795 million people still go to bed hungry every night. Matthew 25 tells us when we serve the least of these, we are serving the Lord. As people of faith, we cannot turn our back on those in desperate need.
"As followers of Christ, it is our moral responsibility to urge you to support and protect the International Affairs Budget, and avoid disproportionate cuts to these vital programs that ensure that our country continues to be the "shining city upon a hill."
