President Reagan, seeing for himself the devastation brought to farmers by this summer's drought, Thursday told those hard hit by the dry spell, "We can't make it rain, but we can help to ease the pain."

Reagan spoke to an audience of 200 or so gathered under a shade tree at the fairgrounds here. To his back was a field of corn, green from recent rains but still shriveled by the lack of moistute.Minutes earlier, Reagan had walked through corn and soybean fields on Herman and Richard Krone's 2,800-acre farm. Reagan towered over the corn, normally 8 feet high by this time of year but less than half that height. Soybeans plants were a quarter of their expected size.

"What I saw was not a pretty sight," Reagan told his audience.

Earlier, Reagan had spent 25 minutes in the presidential helicopter inspecting fields from the air.

He noted the rains that had come to southern Illinois in recent days. The rain, up to 4 inches in places, "may have helped . . . but it hasn't solved the problem," he said.

The White House has said that Reagan would sign relief legislation making its way through Congress, provided that cost-raising amendments are not tacked on.

Asked about the amendments - more than 30 in each house and covering a variety of special interests - Reagan said, "I hope that they're not being tacked on. I hope they are not getting away with it."

The White House said Reagan feels two forms of legislative help are essential for farmers had hit through much of the nation:

-Aid for farmers who have received advance deficiency payments, which are advances on what a farmer expects to receive from the government after harvest.

"As of now, many drought-stricken farms will have to refund this money," the announcement from the White House press office said.

-Help for suffering farmers not covered by the advance-deficiency payment system.

The White House also noted that "the president has been working closely with the leadership of the House and Senate agriculture committees and with governors from farm states to draft timely, bipartisan legislation to help the many farmers who will suffer substantial losses."

Although Krone's farm has had nearly 2 inches of rain this week and some parts of southern Illinois have had rain recently, agriculture experts say the rain won't do much to help the already shriveled corn crop.

"Even though it has rained, when the president looks at the crops, he's going to see a bad situation," said Steve Newman of the Illinois Farm Bureau, before Reagan's visit.

At the 2,800-acre Krone farm, about 400 acres of the 1,200-acre corn crop are believed to have been irreversibly damaged, for a financial loss estimated at $35,000. Krone said corn stalks that should be 10 feet to 12 feet high by this time of year measure only 2 feet to 5 feet, with burnt, brownish tassels.

The dry spell also has parched 125 acres of pasture used to feed Krone's 150 head of cattle.