Anthony Jordan, the executive director of the Baptist General Convention, asked Gov. Frank Keating and legislative leaders to "stop the lottery in its tracks."
Jordan said a lottery is a system of raising state revenue whose only product is grief.
His comments came at a news conference organized by Rep. Forrest Claunch, R-Midwest City, who led opposition to a 1993 lottery proposal that was defeated at the polls.
The latest lottery plan passed a subcommittee on Monday and headed for an afternoon vote in the Senate Appropriations Committee.
Jordan said there are 750,000 Baptists in Oklahoma and they will be a force if the lottery proposal ever got on a statewide ballot.
Rep. Lance Cargill, R-Harrah, member of an Assembly of God Church, said ministers in his denomination would also rally opposition.
Jordan said he was disappointed that the measure was sponsored by a fellow Baptist, Sen. Brad Henry, D-Shawnee.
He said Henry was right to try to raise money for education, but was wrong on how to do it.
He also noted that Henry had acknowledged that using gambling proceeds was a bad way to fund government.
Ralph Bullard, head master of the Christian Heritage Academy, said that as a private school administrator, he knows the pressures of financing education, but he would never consider using gambling proceeds.
Claunch said he did not know how Henry's bill would fare in the Senate, but said it had no chance in the House.
He disagreed with Henry's claim that it would raise $500 million for schools and college scholarships.
Henry later said the $500 million figure is a conservative estimate, not counting the cost of prizes and other expenses.
The Shawnee senator said that although he has been philosophically opposed to the idea in the past, Oklahoma is losing revenue to Texas and other surrounding states that have lotteries.
Claunch contends a lottery would open up Oklahoma to casino gambling on Indian land, an argument that Henry disputes.