A Pentagon executive seemed to be constructing an escape hatch yesterday for President Reagan's announced plan to put the first batch of MX missiles in vacated Titan holes, saying this was merely an example of where the new land missile might be deployed.

When the plan was announced at the White House last Friday, Defense Secretary Caspar W. Weinberger told reporters that some of the MX missiles "will replace the Titans because under the budget reduction plans we will be taking the Titans out of service." At an earlier Pentagon briefing, reporters were told that 36 Titan silos probably would be rebuilt for the MX because the old missiles had been deployed in groups of 18.

But Weinberger ran into a storm of protest at congressional hearings this week when he said substituting MX for Titan would be a partial answer to the growing vulnerability of land missiles. Weinberger said the rebuilt silos would be hardened to withstand a blast exerting a force of up to 5,000 pounds per square inch.

Yesterday, however, Marvin Atkins, Pentagon director of offensive and space systems, said of the MX deployment: "There has been no decision whether to put them in Minuteman or Titan silos or both, or how many missiles will be in place." He termed the use of 36 Titan holes for MX as "simply examples" of possible future deployment in talking to reporters after a briefing for lawmakers from Arkansas and Kansas, two of the three states where Titans are deployed.

"We need to find out how much additional protection, how much hardness against Soviet attack you can buy for a given amount of money," said Atkins. The study will take about a year to complete, he added.

A 22-page fact sheet that the Reagan administration handed out on Friday, entitled "The Reagan Strategic Program," sounded less equivocal, stating:

"In the near term, we will deploy a limited number of MX missiles as soon as possible in Titan or Minuteman silos that will be reconstructed for much greater hardness to nuclear effects. Although specific base locations are still under review, the most likely site for the initial MX deployment is an existing Titan base. All aging Titan missiles will be deactivated as soon as possible . . . . Initial deployment in existing ICBM silos is the only way to avoid delaying MX. We cannot afford to put off MX . . . . "

Sen. Robert J. Dole (R-Kan.), whose home state of Kansas has Titan silos, said after hearing Atkins: "I think it's fair to say that no decision has been made on when they'll be deployed, in which state, and whether they will go into Titan or Minuteman silos."

Rep. Dan Glickman (D-Kan.), whose district encompasses some Titan silos, said: "I think it's fair to say that even at top levels of the Department officials changed their minds fairly recently." The Wichita Democrat said it may turn out that the MX will not be placed in silos at all, or deployed in them only for a short time to serve as "a bargaining chip" for arms control negotiations.