MCI Communications Corp., a Washington-based long-distance telephone company, is spending $10 million to set up radio paging services in the Northeast and Southwest.

The Federal Communications Commission approved plans for the paging system, to be operated by an MCI subsidiary, MCI Airsignal, in New York City, Boston, Hartford, Conn., Phoenix, Tucson and Tulsa, company officials said yesterday.

The system should be operable in two or three months, company officials said.

Airsignal President Gerald H. Taylor said the planned paging service will feature hardware that differs substantially from the conventional beeper alarm.

MCI pagers will be equipped with 40-character memory, meaning they will be able to store 40 individual characters or digits, enabling the instrument carrier to receive telephone numbers, stock quotes or cryptic word messages.

Basically, the system will work like this: Pagers will have individual telephone numbers. Touchtone phones will be used to contact the pagers and to send signals that can be translated into numbers or letters. Messages will be stored in the pager's memory and relayed through liquid crystal displays, such as those on digital watches.

The pagers have a two-way, adjustable alarm--tone alert and light signal--to notify the receiving party.

"High tech has come to the paging industry," Taylor said. He said the MCI system eliminates the guesswork that characterizes use of conventional beeper pages. "You no longer have to run around trying to find out who is calling you. The liquid crystal display message tells you that."

Individual use of the MCI paging system, including rental of a single pager, will cost about $30 per month. The pagers can be bought for $350, in which case, the system rental fee for an individual can be reduced to $10 or $15 a month, Taylor said.