Senate Armed Services Committee Chairman John C. Stennis (D-Miss.) yesterday said that in the wake of last week's Titan II explosion "we . . . need to seriously explore what alternatives we have for replacing this missile as soon as practible."

In a Senate speech, Stennis cautioned that he was not sounding "an alert or panic call for their elimination from the [strategic] force," but he said a study should be made of possibilities for replacing the 52 remaining Titan IIs "in the near term of the next couple years and in the longer terms as the MX missile comes into the force."

Stennis, who controls the Pentagon's authorizing committee in the Senate and the defense appropriations subcommittee, became the first influential senator to suggest that the 18-year-old , liquid-fueled ICBM be taken out of service before the MX system comes into being six years from now.

Defense Secretary Harold Brown said last Sunday that the administration has no intention of dismantling the Titan IIs before the MX is available.

However, Stennis said yesterday that "it is imperative that we now consider what options we have" for handling the Titans' mission for destroying enemy cities with its giant, nine-megaton warhead.

Altough Stennis said the latest Titan II accident creates "cause for concern," he said his committee would study the matter but has no plans for hearings now.

While commending the airmen who risked their lives in last week's accident in Arkansas, Stennis said "it is absolutely essential" that "another review of the safety of the Titan II" be undertaken.

Four months ago, the Air Force released an internal study that gave the Titan system "good" marks on safety.

Last week's explosion was precipitated when an airman working on the missile dropped a wrench socket, which bounced into the missile and punctured the fuel tank.

Titan safety systems were unable to stem the flow of highly toxic and volatile fuel. About eight hours after the incident began, the fuel exploded, killing one airman, injuring 21 others and catapulting the warhead 200 yards into a pasture.

The Air Force said it will investigate the accident and the safety of the Titan system.

Dr. Hans Mark, secetary of the Air Force, told a House Armed Services Committee on Wednesday that the Titans play a more important role in U.S. strategic policies today than they did when they entered the force in 1968.

Mark said the Titan force represents one-third of the megatonnage of U.S. land-based intercontinental balistic missiles (ICMBs).

Stennis noted yesterday that the rest of the U.S. ICBMs were converted from liquid to solid fuels in the late 1960s "for, among other reasons, ease and safety of maintenance and operation."

In another development, Rep. Dan Glickman (D-Kan.), whose district contains several of Kansas' 18 Titan II missile sites, said yesterday that Air Force officials had told him that two specific safety changes had been ordered in the wake of the Arkansas accident.

The first will require that wrenches such as the one that caused last week's accident either be attached to the person using it or to a fixed object. The second change will require that a second platform exist under any area where someone is working on a missile.

In the Arkansas accident, an eight-pound wrench socket went through a rubber mat on work platform that was supposed to keep it from falling.