For years, I have been frustrated by news stories that mix bushels and tons, or gallons and tons, and expect me to know what they mean.

For example, I may read: "Outer Mongolia today announced it is cutting the import agreement under which Monaco was to have shipped 10 million metric tons of wheat to Outer Mongolia. Minister of Agriculture J. Worthington Foulfellow said 20 million bushels would be trimmed from the agreement."

The reader is left to wonder, "How do I relate a reduction stated in bushels to a contract stated in tons? How many bushels to a ton? By what percentage was the contract reduced?"

Last week I read another of these stories and vowed I'd find some way to relate tons to bushels or gallons.

I set the alarm for 11 a.m., and when it went off I began calling people at the Department of Agriculture.

The public affairs office seemed a logical place to begin, but the man I wanted there had just gone to lunch.

I tried another office, but the man there who could have answered my question had also just left for lunch.

The next man I called was out of town. The next office put me on hold until I almost fell back asleep.

I tried another man and found he had just left for lunch. By that time, it was 11:25.

I dialed Orville I. Overboe's number. He's a program specialist with the agricultural Stabilization Conservation Service. When he answered the phone, I almost blurted out, "How come you're not at lunch?"

Fortunately, I didn't. Instead, I asked, "Is there a rule of thumb relationship between bushels and tons of grain?"

"Yes," he said. "Wheat and soybeans weigh 60 pounds to the bushel, corn weighs 56 pounds, and so on. To translate bushels into tons, you'd divide the weight-per-bushel into 2,000; to translate bushels into metric tons, you'd divide into 2,204."

So now there's no longer any mystery to the grain import stories I read. Inasmuch as 60 goes into 2,204 about 36.7 times, 10 million metric tons of wheat would be about 367 million bushels. A reduction of 20 million bushels in a 367 million bushel contract would be rather insignificant.

Frankly, I hadn't realized that a bushel of wheat weighs so much, or that only 37 bushels weigh more than a ton, or that so many employees of the Department of Agriculture are at lunch by 11 a.m. I guess they're all former farm boys. POSTSCRIPT

Oil stories that hop back and forth between tons and barrels are also confusing to readers. This is especially so because barrels come in a bewildering array of sizes.

However, barrels of oil come in only one standard size -- but that's because oil doesn't come in barrels, so it's easy to standardize the barrels it doesn't come in.

The oil barrel is an "artificial designation" that dates back to 1866. You can thank Jim Walters, measurement coordinator for the American Petroleum Institute, for that fascinating piece of information.

Jim says that shortly after oil was discovered near Oil Creek, Pa., 30 major producers there were selling it in barrels of 30 different sizes. Dr. M. C. Egbert called the 30 producers together and got them to agree on one standard barrel of 42 gallons. The United States Geological Survey made it official in 1882.

But oil producers outgrew their barrels a long time ago. Today, they fill a supertanker with 500,000 tons of bulk oil. Thereafter, that cargo can be referred to in terms of tons, barrels or gallons, but the relationship between gallons and pounds varies with the quality of the oil.

Crude oil from Albania averages about 6.6 pounds per gallon. Oil from New Zealand averages closer to 8 pounds per gallon.

Jim Walters thinks in terms of an average of 7.25 pounds when he's doing rough calculations. "The' range," he says, "is from 7.09 to 7.85 barrels to the metric ton."

So a supertanker that carries 500,000 tons of oil (some carry more) can be said to carry about 3.6 million barrels, or more than 150 million gallons.

Incidentally, it might be well to clarify the relationship between crude oil and gasoline.

Walters says about 45.5 percent of crude emerges as gasoline of the kind we put into our automobiles.

What happens to the other 54.5 percent? Almost all of it is turned into something useful -- things like jet fuel (a hefty 6.8 percent), asphalt, heating oil, diesel fuel, lubricating oils and kerosene.

To recapitulate: a ton of crude is the equivalent of just over seven barrels, or about 300 gallons. A ton, a barrel or a gallon of crude will yield less than half that amount in gasoline. When we're short a million barrels of crude a day, we're short 42 million gallons of crude, or 19 million gallons of gasoline.