John Sculley, chief executive officer of Apple Computer Inc., said the company had achieved "a major breakthrough" by getting it's Macintosh computers to respond to commands spoken by people using ordinary language.

Among other things, Apple's technology makes it possible for a person to tell a Macintosh computer to change the type size in a document, program a video-recorder or find a name in an electronic telephone directory and then place a telephone call to that person. Essentially, the technology allows a user to speak aloud any instruction he might give to a Macintosh using a keyboard or mouse.

Leading computer researchers hailed Apple's work, saying it appeared to represent a milestone in the decades-long quest to build personal computers that can carry out spoken insturctions.

"As far as I know, this is a first," said Marvin Minsky, a computer science professor at M.I.T. and a pioneer in the field of artificial intelligence. Mr. Minsky, along with 500 other people, witnessed a demonstration of Apple's technology at the Technology, Entertainment and Design conference in Monterey Friday evening. About 24 hours earlier, Apple conducted a similar demonstration in Tokyo at a trade show.

Several companies, most notably Dragon Systems Inc., already sell speech-recognizers for personal computers, but these products require special hardware and a speaker must "train" these systems to respond to his or her voice. Also, these products work well only when speakers say one word at a time, pausing after each one.

On the other hand, Apple's speech-recognizer responded to continuous speech, even answering back at times. Mr. Sculley said the system works with off-the-shelf Macintosh computers without any special hardware such as a digital-signal-processor chip and immediately responds to a new speaker's voice...

The only potential drawback is that the speech processor, at least today, requires a top-of-the-line 68040 microprocessor which could mean that speech-capable computers would sell for more than $5000.

Kai-fu Lee, the key figure behind Apple's speech research, said the speech recognizer could stand some improvement. Work remains to be done on the interface and the vocabulary could also be expanded. Another problem is making the speech-recognizer robust enough that background noise doesn't throw it off.

Apple's speech-recognizer requires speakers to begin each command by addressing the computer with a prearranged name. Mr. Lee's name for his computer helper, or agent, is "Casper." At one point in the demonstration, Mr. Lee asked Caspar to pay two bills electronically, and he specified the amount of each check. Mr. Lee's request was carried out.