Passion over ice cream is usually confined to the lust for a cold dish of peach to finish a summer's dinner or perhaps the temptation of humble vanilla slithering off a slice of warm apple pie. The simple pleasure of a cold and familiar treat.

But passion of a different order stirs today in the nation's capital. The reason: the government is changing its definition of ice cream. And the question is, will our ice cream still be ice cream?

Yes, say the people who manufacture ice cream and stand to make money with the new definition.

No, say the milk producers, who fear they will lose money with it.

But one thing is sure: the taxpayers will pick up the tab, dollar for dollar in dairy support programs, to the extent that the ice cream industry takes advantage of the change.

All of this involves only 10 per cent of each carton, cone or cup of ice cream, but it is a dear 10 per cent to the milk producers, who feel that tampering with it will be a disaster.

To be sure the government is not taking the cream out of ice cream that stays. What the Food and Drug Administration is doing is ending its basic requirement that 10 per cent be, essentially, nonfat dry milk - what you buy at the store as powdered milk.

Not that ice cream makers have to quit using nonfat dry milk. But they can and use instead other, cheaper substances derived from milk. Leftovers, as it were.

Even today, a small and restricted amount of one of these ingredients may be substituted for nonfat dry milk. Now FDA is removing the restriction and allowing the ice cream makers to use "safe and suitable" substitutes. The only requirement is that those substitutes provide the same amount of protein as today's ice cream.

But this decision, three years in the making the scheduled to take effect June 13, has evoked a cacophony of claims and counterclaims, of predictions of government losses and of doom: an end to Ice Cream As We Know It.

Sen. William Proxmire, Democrat from the dairy state of Wisconsin, warns that "the end result would be a product less desirable in terms of taste, texture and quality."

"I love Proxmire. I think the world of him, but he's being had now," says an FDA employee who preferred not to be named. "We have not lowered the nutritional or technical profile (of ice cream). We've removed the recipe. If I were a milk-producing farmer, I'd bestamping and crying in my beer, too. They had a rather guaranteed market."

"I have never tried to hide the fact that my prime interest is the economic impact on the American market," says the secretary of the National Milk Producers Federation, Patrick B. Healy. He embellishes that interest with claims of "cheap chemicals," "less nutritional value," anti-import statements and expressions of sympathy for the U.S. taxpayer, who last year paid $116 million to buy surplus nonfat dry milk from farmers.

There are 441 million pounds of the stuff in government stocks now. The Agriculture Department sees about 293 million pounds being displaced from ice cream, at a government cost of $183 million.

"Anything that lessens the commercial demand," says Healy, "lessens the opportunity for (milk) prices to rise above the support level" - the price the government pays for milk that can't be sold. Prices received by farmers have been at that minimum support level since 1975.

Says Robert Mulligan of the International Association of Ice Cream Manufacturers: "From an industry's economic point of view, (the change) could and should give some flexibility to manufacturers to use some ingredients that are nutritious, an apportunity to make a better product, an apportunity to use a waste product and hopefully a positive impact on the cost."

His association asked the FDA for changes in the old standards for ice cream, and the Department of Agriculture predicts that use of the cheaper ingredients will bring "little or no price cutting and an increase in manufacturers' profits in the short run." But Agriculture added that with competition, over time, it expects "cost reductions . . . to be passed through to the consumer."

Mulligan said no one yet knows how extensively the ice cream industry will adopt the new definition but "most are not going to change." Primarily "economy" ice creams - 20 per cent of the market - will be affected, he said.

Agriculture has projected that use of the cheaper ingredients could lead to a 2.5 per cent reduction in retail prices - pennies on a half-gallon carton.

It is hard to say when all this will become apparent in the grocery.The milk producers have asked that the new definition be delayed for a public hearing. And some experts feel the traditional formula will be retained those making premium ice creams.

In the end, of course, the judgment is ours as to whether ice cream is still ice cream and whose ice cream is best. It just may be the excuse to get the bucket and beater out again and, to the melody of metal circling in crushed ice, make it at home.