President Reagan's controversial plan to install MX missiles in Air Force Titan missile silos came as a surprise to Air Force Secretary Verne Orr, who did not learn of the decision until 10 minutes after the press had been informed of it, a spokesman for the secretary confirmed yesterday.

Four weeks ago, Orr had assured members of the Arkansas congressional delegation that the administration had no intention of using any of the Titan silos to base the MX, according to Sen. David H. Pryor (D-Ark.), who attended the meeting.

Seventeen Titans are emplaced at the Little Rock Air Force Base.

A spokesman for Orr said it was not until defense officials were 10 minutes into their briefing for reporters at the Pentagon last Friday that a classified package containing details of Reagan's decision arrived at Orr's desk by special messenger.

Gen. David C. Jones, chairman of the Joint Chiefs of Staff, has said that the chiefs were not consulted on "the details" of Reagan's new strategic weapons program and that he believed the MXs would be vulnerable if based in the fixed Titan silos.

A Pentagon spokesman said yesterday that Reagan is not backing away from the idea of installing MX missiles in vacated Titan holes but refused at the same time to be pinned down on the specifics of his deployment plan.

Defense spokesman Benjamin Welles, in response to news stories quoting a Pentagon executive as saying there was no firm plan to use Titan silos, read a statement saying:

"Defense Department officials have been quoted as saying that we have not committed to deploying any specific numbers in any specific silos, and that is correct. However, this should not be interpreted as waffling on the decision. The president has announced his decision on silo deployment, and we are filling in the details."

The first week of congressional hearings on Reagan's strategic blueprint showed that his recommendation to rebuild Titan silos to accommodate the first batch of MX missiles--Pentagon officials estimated last week that 36 MXs will be put in Titan holes--is the most controversial feature. Lawmakers expressed doubts that this hardening would reduce MX vulnerability to Soviet warheads.

Yesterday Chairman Joseph P. Addabbo (D-N.Y.) of the Appropriations defense subcommittee stepped up his attack on another part of the Reagan plan, the recommendation to produce 100 B1 bombers while developing the more advanced Stealth aircraft.

"I am absolutely convinced that the B1 should stay buried, and that resurrecting it will deprive the United States of the timely introduction of the new technology Stealth bomber," Addabbo said in a statement released by his office. "There simply is not enough money to do both."