Heard the one about the talking cash register?

A woman walks into the Grand Union on Rockville Pike, takes a six-pack of soda through the checkout line and a machine tells her, "One eighty."

Shocked, she asks the checkout clerk, "Is that machine talking to me?" The checker nods, collects $2 and punches the register.

"Cash, two dollars. Change due, twenty cents," says the machine, as the transaction flashes on a video screen and is printed on a receipt.

No joke, Grand Union in Rockville's Wintergreen Shopping Center is the first supermarket in the Washington area to install the "POSitalker," a talking computer that uses an actress' voice recorded and transmitted via silicon microchip.

"It's cute," said shopper Lynn Dunnick, a Rockville housewife, who confided, "This is more fun than Giant."

POSitalker, (for "point of sale"), manufactured by National Semiconductor of Santa Clara, Calif., was introduced in San Jose in July 1981.

It currently carries on limited conversations in about 350 stores nationwide.

It costs $300 per unit, is also available in Spanish and French and can be programmed to say "Thank you for shopping with us." But not at Grand Union.

"We prefer our human cashiers to say 'Thank you for shopping with us,' " said Gary Perino, the chain's public relations manager.

"The idea is to get customers through the check-out aisle as fast as possible," Perino said.

The computer's volume is adjustable, too: "In our Dover, N.J., store, which is strictly a senior citizens' community, you can hear the difference. It's rather loud."

Starting today, the Rockville store's video scanner will read the price coding on the side of 90 percent of the products, then relay the information from the electronic eye to a minicomputer, which will send a message back to the video display and to the "POSitalker" (nicknamed "Polly" by the checkout clerks) in one 124th of a second.

Earlier this week, the store's audio components went into action ahead of the video scanners, calling out prices, totals, any credits, amounts given the cashier and how much change is due.

"The poor girl who has to stand there for seven hours would probably lose her mind. But it's effective," said Curtis Karpel, a Potomac lawyer shopping with his wife, Gail.

"It takes some getting used to, but it's great," she said. "They sometimes ring it up wrong or if something's on special. You can catch it when you hear it."

But to some the innovation has eerie Orwellian aspects. "It's insulting," said Joseph LaMarche, a Rockville carpenter. "Pretty soon they'll do away with the humans altogether. It's inhuman. It stinks."

Grand Union's Perino denies that POSitalker will replace jobs and says its installation won't affect grocery prices: "When you're talking about spending $1 million to renovate a store, $300 is a small amount."

Other grocery chains are skeptical about the gadget. Giant has looked at it but thinks the information currently provided consumers at the checkout line is "more than adequate."

A&P nixed it as "a distraction to the customer." And although it has installed them in Richmond and Texas, Safeway has no plans for bringing POSitalker to its Washington-area stores.

Grand Union is undaunted. Donna Sopoliga, corporate point-of-checkout training supervisor, was in Rockville this week to get things rolling, checking "the price integrity of each item in the store" in preparation for today's video-scanner hookup. "We're looking for 18 items per minute." she said. On Wednesday she was reviewing every type of cheese, running packages across the scanner's eye, and working her way toward frozen foods by late evening.

Checkout clerks are accepting the innovation gracefully. "You don't get people charging back, saying you've overcharged them," said Bonnie Fox.

Added John Brosnan, "The voice is more of a hindrance to me. It's distracting. But it's good for the customer. And you tend to tune it out after three days of listening to it."