R. Jeffrey Smith's article "Trident's Mix of Propellant With Warhead Raises Serious Questions" {front page, May 29} in which he discusses the safety of the D-5 missile, contains fundamental errors. The alarmist "the sky is falling" tone he sounds is totally without foundation.

The design technique utilized for the Trident II (D-5) missile has been in use since the late 1970s. The process of optimizing a missile design for the required performance is never routine and involves complex trade-offs to meet performance standards and to comply with established safety criteria.

The relative priorities of safety and missile performance considered during definition of the D-5 weapon system were no different from those used previously. Acceptable standards of safety have always been first priority. The decisions regarding the design of the warhead were made by the highest authorities in both the Defense and Energy Departments. These design criteria are extremely stringent.

Although propellant used in the D-5 has a slightly higher energy output than previous missiles, it is not more likely to initiate an explosion than other propellants used in ballistic missiles. In fact, the material properties of the D-5 propellant are superior to previous propellants.

The environment provided while assembling, handling and storing a Navy strategic missile is highly benign and is fully controlled by established procedures. The missile/warhead assembly process is performed within designated buildings, with specially designed and proofed equipment and by trained and certified personnel to ensure maximum safety.

The Department of Energy, the agency responsible for the nuclear safety of the D-5 warhead, has not informed the Navy of any safety concern. The Navy is also not aware of any effort which would modify the design of either the missile or warhead.

The Trident submarines and missiles provide the most effective strategic deterrent in the world today and for the foreseeable future. The system is unsurpassed in the vital areas of survivability, reliability, responsiveness, flexibility, endurance and lethality. Trident is the keystone to our nation's strategic deterrence and has the full confidence of our national leadership. The safety record concerning sea-launched ballistic missiles is clear evidence of the validity of Navy design practices and provides absolutely no substantiation to the tenor of alarm and concern Mr. Smith tries to instill in The Post's readers. C. A. H. TROST Chief of Naval Operations Washington