Loretta Carrier, a Bowie housewife, was shopping for groceries and a flea collar for her cat one day this week when two Prince George's sheriff's Deputies stopped her and a friend in the parking lot of Collington Plaza.

The deputies questioned them instensely: were they Americans citizens? Did they live in Prince George's County? Were they registered voters? Were they over 18?

"Well, congratulations," one deputy said, "you're now a jury member."

"Right now?" Carrier said, pointing to her bag full of groceries, in blue jeans and dirty tennis shoes?"

"That's right," she recalls the depute saying. "If you refuse you could be arrested.

For 20 or so other Prince George's residents, the message was much the same Tuesday. When a county circuit judge ran out of potential jurors for a murder case he was trying, he sent the deputies out to find some more, and in shopping centers, malls and restaurants around the county, they did their job

By 2 p.m. housewives, businessmen and shoppers who had been going about their business were gathered at the courthouse in Upper Marlboro ready for emergency civic duty. As it turned out, they were not needed, but the sudden roundup has been the talk of Upper Marlboro.

The sudden shortage of jurors was a "fluke," said one court official. Ordinarily jurors are selected from voter registrations rolls and informed well in advance of their two-week jury service. Usually there are 100 jurors in the courthouse each day ready to hear cases. But a combination of too many trials in progress and the large number of "strikes" (jurors eliminated by the defense or prosecution) led to the unusual crunch. For the first time in five years, said sheriff's officials, they were ordered to scour the streets for men and women who would judge their fellow citizens.

In this case, 50 potential jurors had been questioned. The defense challenged some. Others were challenged by the state. Some were excused by Judge James H. Taylor. But when it was over, only six of the necessary 12 had been chosen.

Judge Taylor looked over at the sheriff's deputy guarding his courtroom. "Mr. Sheriff," the deputy recalls being told, "go out and get me 15 or 20 jurors off the street." The startled sheriff's deputy headed for his office. "It's a court order," he explained later, "what the judge says, you do."

The great jury roundup was under way, and nearly a dozen sheriff's cars fanned out all over Prince George's County.

"It used to happen with great regularity around here," said one sheriff's deputy, if you happen to be some poor slob cashing a check across the street, the next thing you know you're a juror."

Renee, Box, 21, of Clinton, was at Marlboro Plaza on an errand from the feed supply store where she worked. "This is our busy season, and we are short of help," Box said yesterday. "I parked my car and a sheriff's deputy came up and asked me several questions."

The deputy told her she was needed immediately as a jury member in a murder trial in Upper Marlboro.

"But I'm working," Box said.

"Doesn't make a difference," the sheriff's deputy told her.

Box put her head down on the car. "This couldn't be happening, I thought. I've got to work."

According to sheriff's officials, one citizen even called the county police department to complain that deputies were harassing citizens at malls. The police sent a car to investigate.

By early afternoon, however, a jury in another courtroom returned a verdict and was available for work. Several of its members were recruited to fill out Judge Taylor's jury and those who had been rounded up were sent home.

"Judge Taylor was just peeved and impatient," said one informed source. "Jurors would have been available when he needed them."

During a court recess yesterday, Judge Taylor said he had acted properly in ordering the sheriff to round up more jurors off the streets. "All I know is that I ran out of jurors; I'm allowed to do it, and I did it," he said.