Phoenix disc jockey Bobby Butler, South Dakota advertising man Sheldon R. Songstad and Sen. George McGovern (D.S.D.) have something in common these days.

All three want the United States to exploit more forcefully the advantages that come with being the world's largest grain exporter.

In song, bumper sticker and speech, they have been advocating higher wheat prices, perhaps even wheat prices pegged to oil prices-and possibly creation of a cartel to apply leverage worldwide.

"Cheaper Crude or No More Food," a country tune sung by Butler and written by Brent Burns, contains the none-too-subtle suggestion that grain prices be tied to oil prices-a step that would hike U.S. wheat prices from their prevailing $3.50 a bushel to around $16 a bushel.

The song has become the rage of the Midwest since it was broadcast by radio commentator Paul Harvey and mentioned on ABC's "Good Morning America."

Songstad, a Republican former state senator from Buffalo Ridge, S.D., had bumper stickers printed at his own expense reading, "A Bushel of Grain for a Barrel of Oil."

The advertising man said he "wanted to be that one little voice in the dark that speaks out." So far he has circulated $1,500 stickers and has received requests for thousands more. In Iowa on Friday, President Carter told local officials he supported a swap of U.S. farm products for Mexican oil and said he'd take this up with Mexican officials Saturday in Los Angeles.

In a Washington interview, McGovern called last week for a Canadian-American "deal" in which the world's two leading wheat exporters would fix a floor price of$5 a bushel.

How far these dreams of a wheat windfall are from becoming reality is expected to be illustrated Thursday when the world's leading wheat-trading nations convene a summit in the remote town of Saskatoon, Saskatchewan.

Unlike the meetings of the world's oil ministers, preparations for the Saskatoon summit are going forward with little fanfare and few expectations that the exporters will take any cartel-like action to exploit their domination of world grain markets.

The Saskatoon meeting will be the first high-level session on wheat since international talks in Geneva last winter between exporters and importers ended without agreement on a plan to stabilize world wheat prices.

Attending will be representatives of the United States, Canada, Australia and Argentina, which account for about 85 percent of wheat exports. The fact that importing nations haven't been invited has raised some fears among them that the exporters might try to form a cartel similar to the Organization of Petroleum Exporting Countries (OPEC).

But U.S. officials say the main hope is for some agreement among the big four to avoid a price-cuttiing "wheat war" in the months ahead, as they attempt to dispose of the largest unsold surpluses in a decade.

This will require some agreement among them on equitable shares of world markets; on steps to limit production as a means of controlling the growth of surpluses and on sharing information.

Clouding the preparations is the suspicion among some participants that the meeting has been engineered mainly to promote the political fortunes of Otto Lang, the Liberal minister in charge of wheat marketing policy in the Canadian cabinet.

Lang is facing a battle for his seat in the May 22 parliamentary elections. His home town is Saskatoon, which has given rise to press suggestions that it was chosen for the summit to buttress his prestige locally.

The European Common Market, which exports significant quantities of wheat, declined to send a representative to the meeting. One U.S. official said that Australian officials have informed Secretary of Agriculture Bob Bergland that they would not participate in talks leading to formation of a sellers' cartel.

Australia, which lacks facilities to store vast amounts of unsold wheat, now has record wheat supplies of nearly six million tons on hand. The United States and Canada have approximately 26 million tons and 13 million tons respectively, of unsold wheat.

While officials at the Department of Agriculture and at the White House speak of "cooperation" with Canada, they say that the administration is opposed to a wheat cartel on philosophical and practical grounds.

U.S. negotiators have been lobbying hard for freer world trade while working to reduece OPEC's economic power.

And opponents of a wheat cartel argue that it would fail because foreign countries could grow more food of their own or switch from North American wheat to other food sources, such as Japanese rice, also in suplus.

World wheat imports come to 75 million tons a year, and account for one bushel out of six consumed worldwide. The United States and Canada supply two-third of those imports.

That, others say, is too much for importers to make up by switching to other sources, or by growing more food. Japan has too little land to supply its own needs and many tropical countries where bread has become a dietary staple have climates unsuited to growing wheat.

Most economists agree that an oil-for-grain pricing system would be difficult to enforce. Many oil exporting countries such as Saudi Arabial for example, are thinly populated and don't require much imported grain.

But some say that a cartel that would force all countries to pay more for North American wheat might work. In Japan, a quasi-government agency marks up the price of U.S. wheat up to $6 a bushel before reselling it locally-a fact that has convinced some senators that U.S. wheat is underpriced.

Sen. Henry Bellmon (R-Okla.) has introduced a bill to establish an international grain exporting commission with the power to issue export certificates and charge fees for them. The fees would be passed on to foreign buyers in the form of higher prices, and the revenues would be distributed to farmers. CAPTION: Illustration, If they don't lower the gas, We're gonna lower the boom. Quit shipping all that wheat and corn. Forget the Golden Rule. We've been nice guys long enough, Now it's time to get tough. Cheaper crude. . . Or no more food. - From "Cheaper Crude or No More Food" Copyright (c) , 1979 Brent Burns South Dakota advertising man has had thousands of requests for this bumper sticker he printed. Sheldon Songstad