About 10,000 flood-ravaged acres of Illinois farmland—mostly in the southern part of the state near the Mississippi River—may wind up as federal wetlands under an Agriculture Department program announced Wednesday.

The $15 million Emergency Wetlands Reserve Program was part of the disaster bill passed this year by Congress, but rules were just released on how people can sell their land to the government.

Charles Whitmore, conservationist with the federal Soil Conservation Service in Illinois, estimated that as many as 20,000 acres in Illinois would meet the program’s requirements.

Most of that farmland, Whitmore said, would be concentrated in Southern Illinois, where sand covered croplands to a greater degree than elsewhere, and where a higher concentration of levee breaks occurred.

‘‘It just costs too much to remove that sand from that cropland,’‘ Whitmore said in a telephone interview from his office in Springfield.

Whitmore estimated that about 10,000 acres in Illinois would be offered for the program. How much acreage is purchased must be determined by further review of the applications received by Dec. 31, he added.

Larry Quandt, president of the Illinois Farmers Union, said he hoped the number of acres going into the program would be minimal. Quandt said idling farmland by selling it to the federal government would reduce the tax base in the affected areas, and also slow down economic activity because previously productive farmland would be taken out of use.

‘‘Restoring wetlands, that’s a really good idea. But you have to take into account the other factors. It’s not a win-win situation like it may look on first glance,’‘ he said.

To be eligible, the cost of reclaiming the cropland and repairing any levees must exceed the value of the land itself, which will be decided by the conservation service in consultation with farmers, appraisers, environmental and commodity groups.

The land also must have been planted in crops at least one of the past five years.

Once those thresholds are met, the land owner will be paid for the property and receive at least 75 percent of the costs of returning the wetland to its natural state, according to Agriculture Department documents.