Most Americans believe in a God who answers prayers but some say those prayers won't work unless you pray regularly and believe "certain things."

Those were among the findings in a new USA TODAY/Gallup survey on prayer, timed to Thursday's National Day of Prayer. This year the NDP is a headliner due to a legal challenge and to lightening-rod-for-critics Rev. Franklin Graham, honorary chairman of the private evangelical National Day of Prayer Task Force.

Graham, booted off the prayer event platform planned for the Pentagon for insulting non-Christians, called out President Obama today. He essentially dared the president to get Graham back on the Pentagon program or be seen as insulting Christians. The White House didn't bite -- at least not yet.

Political and theological controversies aside, prayer is a deeply treasured practice for many believers. The survey of 1049 adults, conducted last weekend, also asked some questions about what kinds of prayers are effective.

For some it only works if it's a regular practice: 19% say "Prayer is effective only if a person prays regularly." Others say doesn't have to be regular (14%). But most (60.8%) say how often you pray "has no impact" on whether your prayers will be effective.

The web site for the private "Task Force," which is sponsoring National Day of Prayer events nationwide, claims that while God hears all prayers, you have to be a child of God -- a believer in salvation through Jesus -- for your prayers to be answered.

But most Americans don't agree. About 80% say "prayer can be effective no matter what a person believes in" while only 14.5% say it just works for "people who hold certain religious beliefs."

In an interview Tuesday, Graham mocked Muslims and Hindus and said they "do not worship the same God I worship."

Non-Christians are still very welcome to join in the Christian-only prayers at Task Force events or sponsor their own services, he said. But he doesn't think their prayers are heading the same place as his.

Do you agree? If you pray from the heart, does it matter what religion -- if any -- you claim?