When Consumer Reports last tested cassette tape decks, it rated the Teac A170S at the top of its list. The machine was "a best buy" at its $200 list price, Consumer Reports said, and could probably be purchased at substantial discounts.

Substantial is hardly adequate to describe the discounts being advertised by Washington hifi dealers on that particular model: $119, $117, $111 and $108.

Those prices will probably go even lower during the big Labor Day sales.

Part of the reason is that the model is being discontinued (dumped as they say in the trade) in favor of a new version. And part of the reason is that when the fickle finger of consumerism touched the Teac tape deck it turned it into a football.

Not a real football, but one of those products whose price gets kicked around so much that many people in the trade call it that.

It took a few months. When the Consumers Union ratings first came out, shoppers began asking about the top rated model and dealers discovered that advertising it brought in customers.

Pretty soon dealers start cutting prices and Consumer reports' favorite tape deck became a symbol of the agressive price competition that characterizes the Washington market.

Washington has always been with Gary Pyle, the hifi buyer at Reliable Home Appliance calls "a real good place to buy stuff."

That reputation began because of the way fair trade laws were written. The federal government outlawed fair trade - fixing of retail prices by manufacturers - except where permitted by state law. The District of Columbia was considerably farther from statehood than it is now, so it didn't have any fair trade law.

As Pyle put is "Congressmen and senators didn't want to pay retail for the things they bought," so there was no fair trade in the district, creating a federal haven for price cutting.

One result was the growth of large mail order businesses, using their district address to sell consumers in states where local shops couldn't ignore the manufacturers' prices. As fair trade laws have faded under legal and political opposition, the mail order hi-fi business here has faded too.

One of the biggest of the mail order firms, Discount Sound recently turned itself into a pair of warehouse style retail stores. Discount Sound is run by David Malasky, 24, whose father for years owned Capital Appliance here.

Mail order has become "a no growth business, a dead end" since fair trade went out, said Malasky.

For Malasky, moving away from mail order meant a choice between becoming "a salon type dealer" - a market that Meyer-Emco has pretty much to itself, relying on service, selection and exclusive brands rather than price competition - or joining the fray. He joined.

The fast track stereo market here is dominated by gaints who count their advertising budgets in millions of lines a year and their volumes in millions of dollars.

Determining who's first is difficult, because none of the candidates volunteers sales figures. Relying on Media Records - which keeps track of advertising expenditures, a reliable indictor of volume - is difficult because some of the biggest sellers mix audio and appliance in the same stores and the same ads.

But the front-runners are acknowledged to be Luskin-Dalmo, Georges, German HiFi, Atlantis Sound, Audio Associates and Circuit City.

Against that competition, Pyle describes Reliable Home Appliances - Audio King as "little guys." Although the company holds the current record low in the kick-around-the-A170S-contest, Pyle said the stores are "price followers - we let everybody else climb all over each other, then we come in below them."

Malasky suggests that in many ways the Washington stereo business is not as price competitive as it seems. "It appears to be competitive because a lot of low prices are being advertised," he said, "but essentially a lot of it is bait and switch."

If the low priced item isn't, as they say in the trade, "nailed down to the floor," the discount on the highly recognized brand may be far greater than the discount on most other items.

Using a Consumer Reports "best buy" as a loss leader, or lure, is the sort of tactic that succeeds especially well in an affluent, educated market like Washington, where wiley bargain hunters pride themselves on knowing what is best and where to buy it cheapest.

Turning a top rated product into a football is in fact, a fairly common phenomena with Consumer Reports ratings, some retailers claim.

Consumer Reports officials say they've made no effort to determine what happens after a product is rated. Said David Berliner, CU's director of public relations, "we don't want to know."