WASHINGTON (AP) _ The videophone war has begun.

MCI Communications Corp. announced Wednesday that it will soon market a videophone to compete with one now on sale from AT&T.

Both provide small television pictures of the people at each end of a conversation. But users of the AT&T Videophone 2500 won't be able to call an MCI VideoPhone user or vice versa.

The phones are incompatible with each other. The MCI phone is also incompatible with audio-only models.

Each company sees its product as the one that should become the international standard.

''When we announced our product in January, we said we were willing - and still are - to license our technology,'' said Jim McGann of AT&T. ''If people want to build to our technology, they simply get in touch with us.''

He said the two phone systems use different video and voice compression systems.

MCI will begin selling its phone, made by British manufacturer GEC-Marconi, early next year to MCI customers and later will provide it for the retail market, said Jerry Taylor, MCI president of consumer markets.

It is simple to operate, says Taylor. ''Just place a regular call and activate the video.''

Same for AT&T's phone.

Both are about the size of a regular phone, plug into standard telephone and power outlets and cost the same to make long distance calls as audio-only models.

They both transmit color pictures and allow callers and listeners to interact simultaneously. Neither, however, produces a picture as clear as broadcast or cable television because of the limitations of telephone wiring.

Andrew Moyler, business manager for GEC-Marconi, said his company has conducted experiments in England with the deaf, who, he said, found the phone effective for reading lips and communicating through sign language.

The MCI phone will sell for about $750 while AT&T is selling its for $1,499 at phone centers nationwide.

Sound expensive?

''A whole generation of young people are demanding video technology and I believe that by the year 2001, visual communications will become as important to consumer as wireless communications,'' said Kenneth Bertaccini, president of AT&T Consumer Products.