For 49 of her 50 years, Lois, a cerebral palsy victim , could not speak a word, write a sentence or communicate a thought in any way other than flopping her head to signal 'yes' or 'no'.

Then Howard Batie, a modern-day "miracle worker," came into her life.

Batie, a self-described "Pentagon paper pusher" dabbles in computers as a hobby. So last year, when asked if he could design a system that would allow Lois to communicate via a computer screen, he was immediately intrigued.

The result is the Handi-Writer, a gadget available for less than $1,000 that allows Lois to display words and phrases on a screen by pressing five large buttons connected to a basic Radio Shack computer. The screen can display up to 72 words and an alphabet, and the buttons allow Lois to select the letters and words she needs to form a message.

"This has really opened up a world for her," said Batie, a bespectacled naval officer who dreamed up the invention in the basement of his Herndon home.

Batie's invention is one of more than 900 computer-based devices entered in a contest sponsored by the Applied Physics Laboratory at Johns Hopkins University to help the handicapped through the use of personal computers.

This weekend, Batie and 29 other finalists, several from this area, will display their creations at the National Academy of Sciences in Washington. A grand prize winner (who will receive $10,000) and runners-up will be announced Monday.

Paul L. Hazan, director of the Johns Hopkins project, said the entries used "an amazing range" of ideas to help the blind, deaf, mentally retarded, learning disabled, physically handicapped and persons with neurological and muscular problems.

The contest, launched by the Laurel, Md., laboratory last November, was "pretty ambitious," Hazan admits. "We wanted to focus the power of this new low-cost computer technology on the needs of the handicapped. And we wanted to harness creativity on a national scale, not just from professionals in the field but from the general public too."

Like Batie's computer system, which was custom-made for Lois but could be used by many speechless, physically disabled persons, most of the inventions tried to solve practical problems of the handicapped, Hazan said.

For instance, Reuel Launey, an Arlington physicist, developed a voice-controlled computer that a quadriplegic can use to operate home appliances, a telephone, a typewriter and other office equipment.

Launey's machine, which says "Good morning, human," turns on lights and tells him the time when he wakes up, was made-to-order for David Ward, a suburban Baltimore man paralyzed from the shoulders down.

Ward, who lost the use of his arms and legs after a fall four years ago, sells industrial equipment and was unable to turn the pages in catalogs and price lists after his accident. Launey said he plans to hook up his computer to a microfiche version of the catalogs, so Ward can use his voice to call up the information he needs to conduct his business.

Many of the inventions are new twists on old ideas. Talking computers have been around for a few years, but Deane Blazie, an electrical engineer from Forest Hill, Md., designed a terminal that reads back everything written on the screen, giving the blind easy access to a computer.

Total Talk, which sells for $6,000, has been purchased by a blind judge who uses it for legal research and a history professor who is writing a book with his machine, Blazie said. Mainly, though, it is used by blind computer programmers like Ted Henter, who works for Blazie and used to rely on Braille printouts to verify what he typed.

"It's so fast, it's like reading the information yourself," said Henter, who can understand the computer's robot-like voice at 300 words a minute, about twice the speed of normal speech.

Other examples of computer wizardry on display this weekend include:

An infrared eye tracking system that allows a nonvocal, severely physically handicapped child to audibly express words or phrases simply by glancing at them on a personal computer screen. An infrared camera associates the position of the child's eyes with a specific word and then the machine says the word in a little girl's voice.

A computer that teaches deaf children to lip read by drawing lips, a mouth and tongue on a screen, and moving them to pronounce a word.

A computer the size of a pocket calculator that a deaf person can use in a phone booth to dial home and convey a message to his personal computer at home.

After the contest ends, Hazan said, Johns Hopkins will sponsor a workshop so the inventors can meet businessmen who might want to manufacture their devices and educators who could use them.

"The bottom line," he said, "is getting these programs in the hands of the handicapped."

You can see these inventions from noon to 4 p.m. Saturday and Sunday in the Great Hall of the National Academy of Sciences at 21st Street and Constitution Avenue in Washington. Admission is free.