Already dim prospects for a defense spending freeze faded further yesterday as Senate Armed Services Chairman Barry Goldwater (R-Ariz.) indicated support for President Reagan's military spending plans and Budget Chairman Pete V. Domenici (R-N.M.) said a greater spending level probably is "realistic."

The worsening outlook for holding next year's defense spending at this year's levels came as a blow to Senate Republican leaders' hopes that an across-the-board budget freeze could be linked with selective program cuts to form a massive package of deficit reductions for fiscal 1986.

While remaining outwardly optimistic about achieving a plan to cut deficits in half within three years, Majority Leader Robert J. Dole (R-Kan.) conceded that defense restraint is critical to agreement on other aspects of a deficit-reduction plan.

"I must say much of it hinges on defense," said Dole, adding that Republicans intend to meet soon with Defense Secretary Caspar W. Weinberger, who has been adamant about an increase of 5.7 percent for the Pentagon after accounting for inflation.

Embracing this figure and suggesting that he would be even happier with more, Goldwater appeared to be strengthening his opposition to major defense cuts, even though he once suggested a freeze and later said he was willing to make spending reductions.

He also said he has no intention of proposing specific military funding cuts until after Reagan's budget is officially submitted to Congress early next month.

"He's the commander-in-chief. I listen to him," Goldwater said.

Goldwater's public refusal to propose cuts before the budget is submitted came only moments after Domenici told reporters that he had asked all committee chairmen during a meeting in Dole's office to submit their spending-cut plans by this Friday.

Domenici acknowledged that Goldwater's stand was something of a setback but indicated that he thought the Senate would still make substantial cuts in defense spending.

Asked if the Senate could now achieve its target of deficits under $100 billion by fiscal 1988, Domenici said, "We'll just have to see. There's only a certain amount of latitude. It will be very difficult with those kinds of defense numbers."

Although Domenici has been a prime mover behind consideration of the budget freeze, he said he now thinks it would be "realistic" to come up with a defense figure "somewhere in between" a freeze and the administration's request. Between the freeze and the administration's proposal is a difference of nearly $12 billion in deficit reductions for next year alone.

Regarding committee compliance with targets for cutting domestic as well as defense spending, Dole said the results have been "mixed" so far. Domenici said some have met their targets, others have indicated that they can't and still others have proposed "alternatives."

Asked if the totals so far are anywhere near the Senate Republicans' target of $54 billion in spending cuts for next year, Domenici said, "I really can't tell you."

Nonetheless, he said, he hopes to have enough committee proposals in hand to begin working on a package that can be completed by the end of February, with floor action to be scheduled "soon thereafter."

Dole made a point yesterday of welcoming an assertion Tuesday by House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) that all aspects of the budget were open for bargaining, including Social Security, defense and other matters. He described the speaker as "very forthcoming and very conciliatory."