The chairman of the Joint Chiefs of Staff said yesterday the chiefs were not consulted in advance on "the details" of President Reagan's new strategic weapons program, and that he continues to have doubts about the key proposal to put the first 36 MX missiles into newly hardened Titan missile silos.

Gen. David C. Jones, the chairman, said that he still personally thinks the MXs would be vulnerable in fixed positions and that he would rather make the new missiles mobile, moving them constantly among a number of sites to protect them.

Jones said the chiefs would not fight the president's proposals now that they have been made. Even so, his testimony will plainly be useful to critics of the president's plan, which ran into some heavy going in its first day on Capitol Hill yesterday.

"We did not have an opportunity to go over the package in detail before it was announced," Jones told the Senate Armed Services Committee during its first hearing on the president's proposals.

But in a second session before the House Appropriations subcommittee on defense later in the day he said of the mobile MX missile idea, "I'm not trying to resurrect it. The Joint Chiefs of Staff will support the decision of the commander-in-chief."

Jones' carefully worded testimony appeared to rule out any major rebellion by the chiefs against the president's plan to substitute MX for Titan after rebuilding the old silos. The chiefs earlier had rejected the idea of trying to protect an MX by piling concrete and steel around it rather than make it mobile so it would be hard for the Soviets to hit.

Jones not only seemed to rule out any military revolt but did not even protest having been frozen out of the last-minute deliberations on the president's new strategic plan for the six-year period fiscal 1982 through 1987.

"I had plenty of opportunity to express my views on the package," Jones said in referring to the months of discussion before the blueprint was put in final form. He said he was unable to convince the president and the secretary of defense that rotating from 100 to 200 MX missiles among 1,000 to 4,600 concrete shelters in western valleys would protect the MXs against Soviet attack in the coming years.

The Joint Chiefs of Staff is comprised of a chairman and the heads of the Army, Navy, Air Force and Marine Corps. When they meet as a corporate body they serve as advisers to the president. Their views do not always prevail, as was the case in 1977 when they recommended put-ting the B1 bomber into production. President Carter canceled the program instead, but no chief resigned in response to that decision.

In sharp contrast to Jones' calm acceptance of Reagan's MX deployment scheme yesterday, several senators hammered away at it and vainly tried to get a cost estimate from Defense Secretary Caspar W. Weinberger.

"What baffles me," complained Sen. Henry M. Jackson (D-Wash.), "is that after eight months we end up with a program that you and others have condemned: putting the missiles back in silos. All you're talking about is hardening the fixed silos."

Jackson and other Armed Services members reminded Weinberger that on Jan. 6 he had said the following at his confirmation hearing:

"I would feel that simply putting it the MX missile into the existing silos would not answer two or three of the concerns that I have; namely, that these are well known and are not hardened sufficiently, nor could they be, to be of sufficient strategic value to count as a strategic improvement of our forces."

Weinberger replied that what he meant was that hardening the silos would be no permanent solution to the increasing vulnerability of land missiles. But, the defense secretary said, putting the MX in rebuilt Titan silos would buy two or three years of vital time. The administration, he promised, will keep exploring less vulnerable basing schemes in the meantime.

"Nothing has changed my mind," Weinberger told Sen. Sam Nunn (D-Ga.). "I was talking about permanent solutions," back in January. "Whatever we gain," from readying the Titan silos to receive the MX in 1986 "is worth it."

Several senators and members of the House Appropriations subcommittee questioned whether the Reagan administration would have enough money to pursue as many new strategic programs as Reagan has proposed at once.

"My understanding is that the overall cruise missile program is being slowed down," Nunn said. He said the same thing is true of the Trident submarine program.

Weinberger denied both assertions, conceding that the Reagan administration intends to build only one Trident submarine a year as opposed to the Carter administration's plan to construct one-and-a-half a year. But he said the one-and-a-half timetable was unrealistic, just "a piece of paper" and not a realistic construction schedule.

Chairman Joseph P. Addabbo (D-N.Y.) of the House subcommittee claimed that the advanced Stealth bomber already is being slowed down to provide more money for the B1 aircraft that Reagan has decided to build. The first of 100 B1 bombers are scheduled to go into service in 1986. Weinberger predicted the Stealth would come along between 1989 and 1990.

"We're stretching the Stealth," Addabbo, a foe of the B1, shouted at Weinberger during the crowded subcommittee hearing. "We'll get into that in closed session."

"We're not delaying it by a month," Weinberger snapped back.

The Stealth program is so secret that the public will probably not know for months who is right.

Weinberger said that the six-year strategic program would cost $180.3 billion in fiscal 1982 dollars and $222 billion if inflation lives up to administration estimates. Sens. Barry Goldwater (R-Ariz.) and Harry F. Byrd Jr. (Ind-Va.) endorsed Reagan's strategic blueprint. But Goldwater warned Weinberger to stay away from the idea of put-ting the MX in an airplane, a future basing concept that the administration intends to keep studying.