Forty MXs reportedly will be placed in existing silos

The Pentagon has decided to place the first 40 MX missiles in existing Minuteman silos in Wyoming, Nebraska, and Colorado, the Los Angeles Times reported.

The Defense Department is also expected to order construction of as many as 14 new silos around each existing silo so the missiles can be ''deceptively based,'' or hidden, and moved at intervals from silo to silo, the report said.

The paper said the Air Force rejected a proposal to base the MX missiles at Grand Forks, N.D. - the only site at which a missile defense system may be erected under terms of the present AMB treaty with the Soviet Union - because of unfavorable geological conditions.

It said some or all of 60 to 160 additional mobile missiles will probably be located in the same three-state complex.

The report said the initial decision will be announced March 9.