U.S. agribusiness magnate Dwayne O. Andreas was winding up one of his frequent trips to Moscow last December when he was suddenly invited to a two-hour meeting in the Kremlin with Politburo member Mikhail Gorbachev.

"He wanted to know what the hell he could do about satisfying these United States conservatives," recalled Andreas, the chairman of Archer Daniels Midland Co. "And he wanted storage elevators and soybean processing plants . . . He needs soybean meal."

For his part, Andreas was happy to oblige. With Gorbachev's blessing, Andreas is now negotiating a potential $100 million-plus contract to build soybean processing plants for the Soviets, a deal that some industry experts say would seal his reputation as the "Armand Hammer of the agricultural processing industry."

Getting to know Gorbachev three months before he was named Soviet premier is typical of the political connections that have helped make Andreas, 67, this country's preeminent grain trader.

A frenetic globe-hopper with a taste for life on a grand scale, Andreas has transformed Archer Daniels Midland (ADM)from a money-losing farm supply company into a $4.7 billion a year multinational giant that, on any given day, sells soybeans to Japan, corn to the Soviets and high-fructose corn sweetener to Coca-Cola.

Andreas, too, has been transformed -- from a bankroller of mostly Democratic farm-state lawmakers into one of the great financial "switch hitters" of American politics and a major international political operative with semi-official status.

Andreas was once known primarily as the personal confidant and campaign benefactor of former vice president and Democratic presidential candidate Hubert H. Humphrey. Now, having pumped hundreds of thousands of dollars into the campaign coffers of both parties, he vacations with Senate Majority Leader and presidential hopeful Sen. Robert J. Dole (R-Kan.), plays golf with House Speaker Thomas P. (Tip) O'Neill (D-Mass.) and is building a statue in Decatur, Ill., where his company is based, of President Reagan, who named him to chair a presidential commission on international private enterprise.

"I've always been associated with the biggest things in this industry," said Andreas in a rare interview in his offices in Decatur. "I'm the biggest processor of agricultural commodities in the world. That's why I've been called in all my life. You can't be in this business on this scale without being thought of" by political leaders.

But Andreas' has also known legal skirmishes and controversy. In 1974, Andreas was indicted but later acquitted on charges of funneling illegal corporate contributions to his good friend, Humphrey. Four years later, ADM pleaded no contest to charges of price-fixing and paid $200,000 in criminal penalties in connection with the sale of grain to the Food for Peace program.

Today, much of the controversy about ADM stems from the company's dominance of the ethanol business -- a heavily subsidized industry that critics say has been created by federal legislation heavily influenced by ADM lobbying. Andreas denies that he mixes politics and business, and his company keeps a deliberately low profile in the nation's capital. It is one of the few Fortune 500 companies (No. 74) that does not maintain a Washington office or a congressional lobbyist.

But if ADM forswears the more visible forums of Washington lobbying, Andreas more than compensates through his personal relationships with key lawmakers. One scene where this is played out is the Seaview Hotel in Bal Harbour, Fla., which Andreas has helped turn into one of the nation's power vacation spots.

Andreas is chairman of the board of the Seaview, which in the 1960s was a hangout for Humphrey and Tom Dewey, the former Republican presidential candidate who died there in 1971 after playing a round of golf with Andreas.

In more recent years, such figures as Dole and his wife, Secretary of Transportation Elizabeth Hanford Dole, O'Neill, former Senate Majority Leader Howard H. Baker Jr., former Democratic National Committee chairman Robert Strauss and others have congregated at the Seaview, usually in the last week of December during the congressional Christmas recess.

"It's a hell of a scene," says television commentator David Brinkley, who owns an apartment at the Seaview. "All these politicians sit around the pool and gossip, play golf, go to the racetrack and then go out to dinner . . . I love it."

Andreas, most of these visitors agree, would never be so tacky as to bring up a question about alcohol tariffs or his other business interests. A small, grandfatherly man with an infectious laugh, Andreas mixes the enthusiasm of a midwestern farm boy with the sophistication of a global trader. He is at ease swapping stories about his first-hand dealings with foreign leaders and U.S. presidents going back to Harry Truman.

"Dwayne Andreas just owns me," says Strauss, who serves on ADM's board of directors. "But I mean that in a nice way. He captures the imagination of everybody he touches . . . My God, he's the ablest man in America. He knows more than most people, he reads more than most people . . . He's a man who has always been way ahead of his time."

Dole describes Andreas as "fascinating" and suggests part of his attraction is the Horatio Alger-like story of his agribusiness success. A college drop-out who was raised in a devout Mennonite family in rural Iowa, Andreas parlayed a bankrupt family-owned grain elevator company into a multimillion dollar personal fortune while still in his 30s.

Today, he flies around the world in an ADM corporate jet, controls banks in Iowa and Minnesota, dispenses philanthropy through the Andreas Foundation and owns apartments at the Waldorf-Astoria in New York and the Seaview plus a lavishly furnished house overlooking Lake Decatur. Andreas is paid $800,833 a year as ADM's chairman and owns 5 percent of the company's stock, worth about $104 million.

Andreas said he was raised in a religious tradition that called for "tithing" 10 percent of personal income to the church. And, he adds, "I consider politics to be just like the church."

As a young firebrand in Minnesota's Democratic-Farmer-Labor Party, Humphrey met Andreas through the liberal Farmers Union. In the early 1960s, Andreas effectively ran the Farmers Union Grain Terminal Association, then the country's largest agricultural cooperative.

"That was the disarming thing about Andreas," says Carl Solberg, who wrote a 1984 biography of Humphrey. "Andreas didn't come to Humphrey as a fatcat, but as a co-op man. And in those days, the Farmers Union was the most leftish of the farm organizations. It was right up Humphrey's alley."

Andreas severed his ties with the Farmers Union when he and his brother Lowell were invited to take over struggling ADM in 1965. By then, Andreas and Humphrey had become family friends. Andreas introduced Humphrey to business leaders, paid for the military school education of one of his children and managed Humphrey's blind financial trust. By investing the trust in ADM stock, he turned Humphrey into a near millionaire, according to Solberg.

In 1968 -- before there were federal limits on individual contributions -- he pumped $100,000 into Humphrey's presidential campaign. But Andreas was also learning to hedge his political bets, and, in 1972, while giving $150,000 to Humphrey's abortive primary campaign for president, he chipped in about $200,000 to President Richard Nixon's reelection.

"I talked to Hubert before I gave to Nixon, and he said, 'Dwayne, you'd be a fool not to give money to Nixon,' "said Andreas. "They were good friends, Nixon and Hubert. My God, I carried messages back and forth between them for 10 years."

Some of this money turned out to be embarrassing for Andreas. In April 1972, Andreas gave $25,000 to Nixon fundraiser Kenneth Dahlberg. That money ended up as a cashier's check in the bank account of Watergate burglar Bernard Barker, providing investigators with the first link between the bungled Watergate break-in and the Nixon campaign committee.

In August of that year -- three months after the contribution -- the Comptroller of the Currency granted a valuable charter for a suburban Minneapolis bank in which Andreas and Dahlberg were co-directors. The charter, which was granted over two other applicants, was one of the speediest approvals ever made by the agency, according to figures released at the time. Nixon administration officials denied Andreas' bank had received special treatment, and the incident was soon submerged by the unfolding drama of Watergate.

Andreas looks back with no regrets on what he views as his "innocent bystander" role in America's greatest political scandal. He only contributed to Nixon in the first place, he says, because Tom Dewey, his good friend and lawyer, "put the arm on me." When the Watergate money was later traced to him, Andreas says, "it was like being crapped on by a bird. It didn't bother me a bit."

Andreas' political mystique today stems more from his role as international deal-maker. Andreas was promoting deals with the Soviets as far back as 1954, when he unsuccessfully tried to persuade the Eisenhower administration to barter surplus U.S. butter and cottonseed oil for Russian gold or manganese.

Today, as co-chairman of the U.S.-U.S.S.R. Trade and Economic Council, he makes regular trips to Moscow. "We have good relations, all the businessmen do with the Russians," said Andreas. "They would rather talk with us anytime than one of these diplomats, because we treat them decently, we don't go off and call them names."

John Lofton, the conservative columnist for the Washington Times, recently lashed out at Andreas for co-hosting an "Agribusiness USA" exhibit in Moscow one month after the Soviets shot down Korean Air Lines Flight 007 in Sept. 1983. "American businessmen like Mr. Andreas would gladly do business with the devil if they could turn a profit," he wrote.

"We've got a lot of crackpots here," responded Andreas. "If they the Russians are going to buy corn, soybeans and wheat, do we want them to buy all that from the Germans? Or do we want to participate in that business? They do $44 billion worth with Western Europe and only $2 billion with us."

Andreas' relationship with the Soviets last year lead to the ultimate home run for a political switch-hitter: his personal audience with Gorbachev last December. An engraving of the Kremlin personally inscribed by the Soviet leader decorates Andreas' office wall.

Three months after his meeting, Gorbachev ascended to the top of the Soviet leadership. And a few weeks after that, Tip O'Neill lead the first congressional delegation to meet with the new Soviet premier. When the new General Secretary of the Soviet Communist Party met the Speaker of the U.S. House of Representatives, according to a O'Neill aide, Gorbachev greeted him with one question. "Do you know my good friend, Dwayne Andreas?" he asked.