Twenty-seven persons were arrested at the White House yesterday when they broke away from a tour group to pray on the front lawn, the Secret Service said.

Carol Fennelly, a spokeswoman for the Community for Creative Non-Violence, said the protesters consisted of CCNV members, "street people" and other volunteers. She said the group was "praying for a change of heart and policy on the homeless in America, particularly as it relates to the Federal City College Shelter and the HUD Report."

The shelter, at 425 Second St. NW, is operated by the CCNV and is in need of repairs the group thinks should be paid for by the federal government. The HUD report is a controversial study released last spring by the Reagan administration that the CCNV believes grossly underestimates the number of homeless in the country.

Fennelly said the protesters took a 10 a.m. tour of the executive mansion and were arrested about an hour later when they stepped over a short chain surrounding the front lawn and began to pray.

A Secret Service spokesman said the protesters were leaving the grounds along a sidewalk leading to the Northeast gate on Pennsylvania Avenue when they jumped the chain and walked toward the north fence. He said the protesters were arrested by members of the Secret Service and charged with unlawful entry for entering a restricted area of the White House grounds.

According to Fennelly, who said she saw the arrests from outside the fence, many of the protesters refused to move and were carried away.

One of those arrested, Fennelly said, was activist Mitch Snyder, one of 12 CCNV members who entered their 40th day yesterday of a hunger strike to publicize the plight of the homeless.