CHICAGO (Reuters) - As dry weather tightened its grip on the central United States, experts warned of the dangers of wildfires in parched wilderness areas, grasslands and even along roadsides and in residential areas.

Already nearly 1,200 square miles have been scorched by fires across the country, an area about one-third larger than usual at this time of year, according to the National Fire Information Center in Boise, Idaho.

And early May is normally just the beginning of the fire season, experts said.

While blazes in Michigan, Florida and Arizona have been contained for the moment, new wildfires erupted this week in Minnesota and Indiana.

Four homes were destroyed and eight damaged in a fire in Princeton, Minnesota, near Minneapolis, this week -- the first residences lost to wildfires in the state since 1992.

Firefighters managed to keep a 1,200-acre wildfire near Orr, in northeast Minnesota, from reaching a giant tinderbox in the Boundary Waters Canoe Area, where millions of dried-up trees downed by a freak July 4, 1999, windstorm could fuel a conflagration.

Minnesota forest service officials are weighing proposals to intentionally set fires in susceptible sections of the million-acre park to curtail the risk of an uncontrollable blaze.

Many of the dead or dying trees are propped up against each other, creating what amounts to a massive pile of firewood that needs only a spark to ignite. Canoeists were warned that if a fire breaks out to get in their craft and head for open water.

``It's the worst we've had since 1988,'' Doug Anderson, Minnesota's fire management coordinator, said of the fire risk across the state, where nearly 53 square miles (13,730 hectares) have already burned.

In northwestern Wisconsin, forestry experts cautioned there was the threat of a wildfire on 50,000 acres (20,240 hectares) of National Forest lands where trees were also blown down in last July's windstorms.

``Vegetation can burn, even when it is green,'' one official said. That point was illustrated this week in a small wildfire at the Indiana Dunes National Lakeshore, a 15,000-acre (6,070 hectares) park located southeast of Chicago.

``Firefighters told us it shouldn't have burned,'' said Al Nash, a spokesman at the park, of a blaze this week that jumped a containment line and burned onto a U.S. Steel plant site.

``Humidity was higher than normally seen on fire days, winds weren't strong and we're going through the annual 'green-up' period,'' Nash said.

``We're starting to see the effects of a drought,'' he said of the park that winds along Lake Michigan among major steel plants, a power plant and thousands of beachfront homes.

The outlook was ominous across the country.

Very high to extreme fire dangers were seen in Arizona, New Mexico, Utah, Oklahoma, Texas, Michigan, Minnesota, and Wisconsin, said Lorraine Buck of the National Fire Information Center. Florida has reported eleven large fires and hundreds of smaller fires through the end of April.

According to the National Weather Service, La Nina, a weather pattern caused by colder-than-normal surface waters in the western Pacific Ocean, may persist and maintain warm, dry conditions in the central and southern United States.

The effect was being felt by farmers and ranchers in the central Corn Belt states where there were fears of a repeat of the severe 1988 drought.

Though midwestern growers reported corn seedlings are beginning to sprout, a lack of subsoil moisture could doom the crop. This year's wheat harvest in Kansas, the nation's top-producing state, was expected to be down 12 percent. And infestations of crop-devouring insects may be worse than usual due to the mild winter.

``The drought starved that wheat over too long a period,'' said Ben Handcock, who was leading journalists on a tour of Kansas wheat fields as director of the Wheat Quality Council.

In other parts of the nation's midsection, recent rains have alleviated some concerns about range fires.

But in hard-hit Missouri, between one-quarter and one-half of the pastureland may be lost.

``A lot of people think the drought has killed their pastures, and it's time to replant,'' said Rob Kallenback, University of Missouri forage specialist, who added he thought some of the pessimism might be ``premature.''