The alarm sounds in Charelle Mariette's Bronx apartment at 5:30 a.m. weekdays, giving her two hours to dress, eat breakfast with her tow teen-agers, catch a "D" train and shove a plastic computer card into a PSDS (Postal Source Data System) clock at the Morgan General Mailing Facility here.

For Mariette, punching that clock signals the beginning of another "game of management versus the workers."

"It never really ends," Mariette said, expressing a sentiment shared by many other postal workers here. "I play eight innings, maybe 10 if I get overtime. If I make it through the day, I win. I'm happy."

Mariette is one of 21,000 active members of the New York Metropolitan Postal Workers Union -- the nation's largest postal local and the largest branch of the American Postal Workers Union.

The Morgan facility handles 9 million to 12 million pieces of letter-sized mail and 3 million to 4 million parcels every 24 hours. Of that amount, Morgan's employees -- 6,800 line workers and supervisors on rotating, eight-hour "tours of duty" -- will process 5 million to 8 million pieces of mail for delivery.

Mariette keys zip codes into a computerized multiple position letter sorting machine at one letter per second or 60 letter a minute. The letters speed by at a dizzying pace, moving to the rhythm of the machine's whirr. Every 30 minutes, Mariette will switch over to stacking letters manually to feed the machine, while another member of her crew relieves her at the keyboard.

By the end of her day, Mariette will have processed 6,700 to 7,200 pieces of mail -- the higher number if she is keying to her machine's 98 percent sorting accuracy. All the while, she will work under the watchful eye of a supervisor who will monitor her accuracy on a zip mail translator.

It is not the type of job that lends itself to creativity. It's a monotonous, piece-work job that lends itself to boredom.

"It's sort of like working on an assembly line in an auto plant," said C. S. Charlie Jones, 52, operations manager of the Morgan facility. "We've tried all kinds of ways to relieve this boredom. But a lot of the jobs are very routine, and it's difficult to combat feelings that come from that."

Not so, says Mariette. "They could start by saying, 'Hey, Miss So-and-So; hey, Mr. So-and-so, you did a nice job today. We're all here for the same purpose, to get the mail out, and you all really helped us to do that today.'

"But that very seldom happens. Instead, we get: 'Hey, you SOB, this machine has a 2 percent error factor and you're screwing up 3 percent. You're messing up production.'"

Like many of her colleagues here and elsewhere, Mariette says she shares postal management's concern for moving as much mail as possible as quickly and accurately as possible. "That is what I'm paid to do and that is what I try to do," she said.

But she and many of her fellow workers argue that their safety, emotional amd career growth needs frequently are trampled on in the rush for production. They claim their initiative on the job in stymied by supervisors who ginore work force suggestions that could increase mail flow. And they argue that with an average salary of about $21,000, especially in expensive New York, they are underpaid and generally underappreciated for what they do.

They also are at a higher risk of injury than workers in many other industries. "Safety in the United States Postal Service is not equal to productivity, quality, cost and other aspects of managing a business," reported a 1980 USPS-commissioned study by the applied technology division of E. I. du Pont de Nemours & Co.

As if to support that contention, Robert Villanueva, a Morgan mail handler, was slightly injured in a work-related incident the day before a reporter visited the facility. A cable snapped on a conveyor belt loading mail bags into a delivery truck. The extendable portion of the apparatus shot out, striking Villanueva in the legs. Safety officials said the accident could have been avoided if the belt had been routinely inspected.

Postal officials say they are doing their best to reduce USPS' 5.5 percent rate of lost workdays due to injuries, a rate nearly double the national industrial average. There has been some progress. Injuries per 100 postal employes dropped 9.1 percent last year, according to the Postal Service's 1980 annual report.

However, the officials concede that there are other aspects of postal work, especially at the processing level, that are difficult to improve. Low morale as a result of boredom is one.

The problem doesn't lend itself to easy solutions, as the postal Service strives to put itself in the black by cutting back on its labor costs and increasing the productivity of its remaining workers.

"We understand the problem," said Mariette. "But if they don't come out to the work floor and talk to the people doing the job if they don't do a better job of respecting and using our intelligence, yeah, we will go under . . . . I'd prefer to play with them, instead of against them, but not too many of them seem to understand that."