The Navy has fewer nuclear submarines and missiles at sea today than at any time since 1967, mainly because of delays in production of its costly and controversial new sub, the Trident.

The Navy had planned, under terms of the first strategic arms limitation treaty of five years ago, to start withdrawing its old Polaris submarines from sea duty and replace them with Tridents. It has now in fact withdrawn two Polaris subs on schedule. But it has no new Tridents with which to replace them.

For the first time since 1967, when the last submarine designed to carry first Polaris and later Poseidon missiles entered the fleet, the Navy's atomic-powered undersea force has dropped below 41 vessels.

The United States in August, without fanfare, began dismantling two of the oldest Polaris subs, essentially removing 32 nuclear-tipped missiles from the U.S. retaliatory force. It was originally intended that the first of some 14 Trident submarines, which are supposed to replace the bulk of the older force, would be undergoing sea trials at about the time the Polaris subs were coming out of service.

But the scheduled delivery of the first Trident is now 26 months behind the April 1979 date called for in the initial contract. That first vessel is now slated for delivery late in June 1981, and sea trials, during which the Navy first checks out the warship before it is officially delivered, has been pushed back until next spring at the earliest.

Navy officials say the target responsibilities of the missiles on the two retired Polaris subs have been shifted to some of the 1,053 U.S. land-based missiles. But they say that the time lag left by having to take them out of service without the Trident replacement is putting a strain on submarine operations in the Pacific.The first Trident sub will be deployed in the Pacific Ocean.

Trident is the biggest single U.S. weapons project to date, with the government spending $28.7 billion, according to Navy figures, to build the 14 new vessels plus 24 missiles to go on each of them, plus facilities to handle them. The Trident missiles are also being installed on some older Poseidon submarines -- each carrying 16 missiles -- and the missile portion of the program is proceeding on schedule, with about four such Trident missile-equipped vessels already on duty in the Atlantic.

Within the administration, defense specialists privately express a sense of outrage with the continuing delays and problems in the submarine itself, a project which is supposed to represent much of the country's future front line of defense. They also express no confidence that the Pentagon has seen the last of these delays. There have now been four delays since the contract was signed six years ago with the delivery date for the first vessel, the USS Ohio.

In March of this year, the prime contractor, the Electric Boat Division of General Dynamics Corp. in New London, Conn., told the Navy the first Trident would be delivered in January 1981, which would have allowed sea trials in July 1980. But in September, the company told the Navy of another five-month delay, pushing delivery back to June 29, 1981, and sea trials until next spring.

Under terms of the 1972 SALT pact with Moscow, both superpowers agreed to take old weapons out of service when new ones, such as submarines, begin their trials. Both sides, thus far, have been complying with this provision even though the five-year SALT agreement has expired and no second SALT pact has been ratified.

The Navy, therefore, felt required by the treaty to begin dismantling two old 16-missile Polaris subs to compensate for the Trident sea trials that were supposed to begin in July, according to Navy testimony before Congress. But when it became apparent that there would be further sea trial delays, the Navy decided to go ahead with the Polaris dismantling anyway because the two older vessels -- the USS Theodore Roosevelt and Abraham Lincoln -- were out of nuclear fuel, would have needed extensive and expensive repair work to stay in service, and because shipyard schedules had already been arranged.

The lengthy delays in Trident are alternately blamed on both the Navy and its contractors. The Navy blames the first two delays on internal management problems at Electric Boat and a shortage of skilled workers there. The third delay is blamed on repairs needed to equipment furnished by the government for the vessels. The latest delay is also, according to the Navy, a result of modification of government-supplied equipment and modifications of the design.