AS A PUBLIC speaker, the president has shown himself over the years to be a master of government horror stories of the "end-to- end" type, as in, "Placed end to end, the (dollars wasted, forms required to be filled out, regulations printed) by Washington would stretch from here to (Mars, Jupiter, the Dog Star Sirius) and back again." This is a useful method for making stupendous numbers comprehensible, and Mr. Reagan will probably have occasion to make more use of it in the near future as the federal budget approaches one trillion dollars, which is to most of us simply a number with 12 zeros.

Last week the Office of Technology Assessment, perhaps believing no one was going to pay much attention if it did nothing more than rattle off a few 10- digit numbers in its presentation to Congress, took a page from Mr. Reagan's book. Expressing its skepticism about some space projects that would cost approximately $2 billion each, the agency produced a study showing that $2 billion would, among other things: make up a stack of bills reaching 140 miles above the Earth's surface; buy every man and woman in Alaska a $5,000 car; weigh about 40 million pounds if it were in $1 bills; pay for another World Trade Center like the one in New York.

As this "Ripley's Believe It or Not" approach to government becomes widely accepted (and unless the numbers start getting smaller, it will have to be), exchanges such as the following will probably be common in congressional hearing rooms:

"And so, Mr. Chairman, the Costa Mazuma water project would come to a total of one billion, three hundred and fifty million dollars, give or take a . . . "

"Please be specific, sir. Do you mean enough $20 bills to fill the Houston Astrodome to the mezzanine level?"

"Yes, of course. Or, put another way, it would purchase enough peanut butter to cover a slice of bread the size of Wyoming."

"I wonder, then, why your department first estimated the project could be done for only 10 stacks of dollar bills reaching to the altitude of an airliner in flight between Los Angeles and Honolulu"

"Well, costs have risen in the interim, but the difference we're talking about is really no more than a roll of Susan B. Anthony dollars stretching from here to Bethesda. Incidentally, the land irrigated by this project would produce enough beef in one year to make a hamburger the size of New Rochelle, New York."

At this point the hearings would adjourn for lunch. In good time, most of us would probably reach a better understanding of what a billion is. The trillion will take a little longer.