President Carter listened sympathetically yesterday as Pentagon executives pleaded for a sizeable increase in the new defense budget but he held off approving final figures until after hearing from other departments later this week.

The basic question before Carter is whether to boost Defense spending 3 percent after inflation when he is demanding austerity in other programs to keep the government's total spending deficit in fiscal 1980 to no more than $30 billion.

It wa a calm, collected session where we went through the various defense budget options," said one participant. "It wasn't a shouting match."

Defense Secretary Harold Brown carried the ball most of the time at the White House meeting, with Air Force Gen. David C. Jones, chairman of the Joint Chiefs of Staff, supplying the military view on various issues discussed, including the controversial MX missile.

A 3 percent increase, after inflation, would give the Pentagon about $123 billion spending in fiscal 1980 and between $135 billion and $137 billion in budget authority-the amount of money that can be committed but not necessarily spent during the year.

Assuming that Congress comes throught with the extra money Carter has said he intends to request early next year for the fiscal 1979 budget, the Pentagon expects to end up spending about $112 billion in the current fiscal year ending Sept. 30, 1979, within a total budget authority of $126 billion. The president has said several times lately that he intends to honor his commitment to NATO partners to increase defense spending by about 3 percent. Some administration officials contend that the NATO pledge has loopholes in it to allow for a lesser increase, a step they favor to dampen inflation.

Offsetting the concern about inflation is the administration's desire to reassure Congress and the public that the nation is keeping up its guard at the same time it is preparing to sign a strategic ams limitation treaty (SALT) with the Soviets,

Secretary of State Cyrus R. Vance flew from Washington to Geneva last night in hopes of ironing out the remaining wrinkles on the SALT II treaty expected to be signed by Carter and sent to the Senate next year.

Congressional critics of SALT II are focusing on the threat increasingly accurate Soviet missiles pose to U.S. land missiles, the 1,054 Minute-man and Titan ICBMs, which stand still in silos rather than move around to make them harder to hit.

To decrease vulnerability, the Carter administration is moving ahead with development of a mobile, land-based missile called the MX, for Missile Experimental. The Mx is expected to receive more than $1 billion total under the fiscal 1979 supplemental and fiscal 1980 defense budgets now getting their final White House review.

However, the president still has not decided how the new MX missile under development should be deployed.Options include deploying each of 200 missiles in a field of decoy holes or putting the weapon inside an airplane.

Air Force leaders, after a series of studies, have concluded that the best option is to put each missile in a field of identical holes to force the Soviets to target each hole with a Soviets to target each hole with a warhead.

The missile would be moved from hole to hole covertly to keep the gunners guessing.

Air Force sources said yesterday that their latest studies indicate that 200 MX missiles could be deployed under this ehll-game technique for about $20 billion, rather than the estimated $30 billion to $40 billion it would cost to move the missile back and forth in a ditch.

To make the shell-game deployment more saleable, the Air Force also has devised ways the Soviets could verify that a field of holes contained only one missile.

Formerly called MAP, for Multiple Aim Point, the new name for the Air Force's shell-game deployment scheme is MPS, for Multiple Protective Structures.

"This is the first time we've designed verifiability into an ICBM," said one Pentagon weapons specialist yesterday in discussing the new features of MPS.

The MX, partly because the ways to deploy it have undergone such lengthy study, is not expected to be deployed until around 1986 or maybe later, even if Carter gives the program the full go-ahead soon.

The House Armed Services Committee has been pressing the Carter administration to make a decision on the MX deployment and is expected to focus on the question during next year's hearings on the Pentagon budget.

Carter, besides reviewing the Pentagon budget, yesterday discussed the SALT II treaty at the White House with the Joint Chiefs of Staff.