When the lights are dimmed at the White House family theater on Tuesday and Thursday evenings, the screen flashes with secret aerial photographs depicting the Soviet military buildup. John Hughes, an analyst with the Defense Intelligence Agency who once briefed President Kennedy on the Cuban missile crisis, narrates pictures of the latest Soviet defense expansion.

In the audience for this twice-weekly production are members of Congress, seeing what could be called "the selling of the defense budget, 1983."

Confronted by growing public skepticism about the size of President Reagan's proposed defense buildup and a Congress poised to scale it back, the White House has launched a counteroffensive that is a mixture of public relations blitz and rescue mission for Reagan's larger national security goals.

The immediate purpose is to put Reagan in a stronger bargaining position for the inevitable negotiating with Congress in the next few weeks over the defense budget.

In the long run, the White House goal is to restore flagging public support for the Reagan rearmament.

Neither goal has been accomplished, and the larger public opinion problem may take months and years of effort, administration officials said.

"The tide is still out, and it hasn't turned yet," one White House official said last week. "Will it? We don't know. The president is totally committed to this, and we're going to do the best we can. We don't know where it will end up."

Still, in an administration that often has had difficulty speaking with one voice on defense spending, the latest White House effort has achieved at least a small victory. Internal disputes about defense outlays have been muted, and a "professional operation," as one official put it, has been put together to carry Reagan's message. "We really didn't have one before," the official said.

The operation was organized by William Greener, a Pentagon and White House spokesman in the administration of President Gerald R. Ford, recently brought in as a consultant to the White House.

Another consultant, Bill Rhatican, a Synfuels Corp. executive taking a leave of absence, begins work at the White House this week to put the plan in motion.

Greener urged Reagan to speak out in a broader context than just defense outlays. "I didn't build the program for the Pentagon budget," he said. "I built it for national security."

Beyond the defense budget, that umbrella covers administration policy in El Salvador, the future of the MX missile, the battle over a nuclear freeze resolution in Congress and arms control negotiations with the Soviets in Geneva. All of them pose troublesome policy and public relations problems for Reagan.

Receiving top priority, because of upcoming budget deadlines, is defense spending. Reagan's 1984 budget calls for the Pentagon to spend about $239 billion, up from $216.4 billion this year, an increase of 10.3 percent after allowing for inflation.

Although White House officials know Reagan eventually must settle for less, their major goal is to strengthen his hand before he sits down to negotiate. This was the reason they sought and received a three-week delay in the Senate Budget Committee markup of the first budget resolution last week.

Reagan's negotiating style is to take a hard line against his critics at the outset and make a deal at the last possible minute. This approach began unfolding again last week when he attacked "liberal" Democrats on the House Budget Committee for a spending plan with only a 4 percent increase above inflation for the Pentagon.

At the same time, he also hinted at "flexibility" in a letter to Senate Majority Leader Howard H. Baker Jr. (R-Tenn.)--a move viewed hopefully by Senate Republicans, some of whom want to halve Reagan's 10.3 percent defense increase.

Sen. Ted Stevens (R-Alaska), chairman of the Senate Appropriations subcommittee on defense, said Reagan seemed "most willing to explore all areas" in regard to trimming the Pentagon budget. But Stevens said "the difficulty is we just haven't developed a consensus" on how to cut about $15 billion from the defense budget.

The administration has not offered to help but may do so as the deadline approaches.

"What we're doing," an administration official said, "is giving the national security guys a chance to prove they can be flexible and to prove their needs."

At the same time, the administration is campaigning for more defense spending with ever-louder warnings about the Soviet threat. "Nothing could bring greater joy to the Kremlin than seeing the United States abandon its defense rebuilding program after barely one year," Reagan said last week.

"Who is going to help us on defense spending?" one administration official asked, answering, "The Russians will." Another official jokingly asked where he could purchase a Prussian helmet to wear to staff meetings.

But officials said they are serious about publicizing the Soviet threat. This has spurred renewed White House interest in selectively declassifying some intelligence reports to reinforce the argument that Soviet advances in weaponry must be countered by Reagan's buildup.

The keystone in Reagan's national security push will be a major speech within the next few weeks centering on defense spending, probably before a foreign relations group in Los Angeles next week. Top White House officials are "unanimous" on the need for Reagan to make such an address, one said.

These officials stressed, however, that the speech would be markedly different in tone from one that he gave recently before evangelical ministers in Orlando, Fla., and is sometimes referred to within the White House as his "Darth Vader" speech. Reagan branded the nuclear freeze a "fraud" and cast the East-West confrontation in moral tones.

Rather, the upcoming speech should be "reasonable and rational," one official said, adding that it should make the case straightforwardly for Reagan's military budget.

"I would like the president to say he has a responsibility. He should say he is not making the speech for political purposes, that he's not doing it for reelection. He should say, 'I'm the commander-in-chief of the armed forces. This is what we face. Given our druthers, no one would spend money for defense, in a perfect world. But it is not a perfect world,' " the official said.

Other aspects of the administration's new national security campaign include:

* Publication this month of "Soviet Military Power," a glossy and well-illustrated pamphlet describing what Defense Secretary Caspar W. Weinberger termed "massive Soviet increases" in military might.

To make sure it attracted wide attention, the administration offered the news media in advance color slides of the pamphlet's illustrations.

Thousands of copies are being mailed, it was hand-carried to members of Congress in advance, and a news conference by Weinberger on the document was broadcast live to Europe.

* White House briefings on Tuesday and Thursday evenings for members of Congress. About 20 members are invited each time for a session that includes the secret photography of Soviet installations. Those who have seen it describe the briefing as particularly graphic and effective, and several officials have discussed declassifying it for public consumption.

* A series of administration-sponsored dinners planned at Blair House for "opinion leaders," at which Cabinet members--including Weinberger, Secretary of State George P. Shultz, Treasury Secretary Donald T. Regan--and others will talk with influential publishers, labor leaders and others about national security and defense issues. Reagan probably will not attend.

* A series of meetings at the White House with former defense and national security officials in Democratic and Republican administrations. The White House has not ignored the recent appeal for $136 billion in defense budget cuts over five years made by former defense secretary Robert S. McNamara, former national security affairs adviser McGeorge Bundy and former secretary of state Cyrus R. Vance, among others.

All of them, and many of their former deputies, may be invited to meet with Reagan on the issue. The White House thinking is that such meetings would at least show the administration's willingness to take its case to its critics.

* Instructions to Cabinet members by Reagan to talk about defense at every opportunity. Even some who privately sought defense cuts in administration councils are saying in public that the Reagan buildup has been trimmed enough.

Staff writer George C. Wilson contributed to this report.