Defense Secretary Caspar W. Weinberger is on the verge of making the two biggest strategic warfare decisions since the missile race went into a gallop with the launching of Russia's sputnik in 1957.

Within days, Weinberger intends to choose the bomber that the United States should build for the rest of this century and probably beyond. Within weeks, he will decide what should be done about deploying a new generation of land-based missiles called the MX.

Whatever he does will be hotly debated, first at the White House and then in Congress.

Billions of dollars, thousands of jobs, political power and perhaps life and death for much of the world hinge on the bomber and MX decisions.

"There is no way you can overstate the significance of these decisions," a former Pentagon executive who did much of the staff work on them said last week. "You're talking about our strategic posture for the next 30 years."

Weinberger says he is aware of this. He says he is deciding what the future holds for "two of the three legs of the triad." Triad is the term for the three types of strategic forces that can hit the Soviet Union with nuclear weapons: long-range bombers, missile-carrying submarines and underground land missiles.

Weinberger is so close to making his decision on the new bomber that he intends to start meeting with congressional leaders on it this week. Senate Armed Forces Committee Chairman John G. Tower (R-Tex.) is scheduled to discuss the new bomber with Weinberger Monday afternoon.

Also, administration officials said the White House National Security Council will meet soon to assess the political as well as military impact of the two bomber options.

Option one is to build an updated version of the Rockwell B1, which President Carter canceled, for the late 1980s, and at the same time start working on a radar-foiling Stealth bomber for the 1990s. Option two entails leap-frogging over the B1 and building the Stealth on a crash basis.

The Air Force is so strongly committed to option one that it formalized it in the five-year budget plan it recently submitted to Weinberger.

The Air Force figures it would cost about $18 billion to build 100 updated B1 bombers and $22 billion for 100 Stealth bombers, a $40 billion total price tag Pentagon insiders say is giving heartburn to Weinberger, the one-time budget-cutter at the Office of Management and Budget.

So much heartburn, in fact, that Pentagon sources said Weinberger directed the Air Force to write a second five-year budget plan showing what the costs would be if only Stealth were built.

The Air Force did sumbit a revised plan, but argued that relying on Stealth alone to take over from the aged B52 would be a risky proposition. Unforeseen technical problems are bound to arise during this march into new technology, Air Force leaders have been warning Weinberger.

Although Stealth aircraft were secretly tested during the Carter administration, they were the size of smaller fighters, not bombers.

Another argument Air Force leaders are using as they fight for the two-bomber option is that going for Stealth alone would mean spending about $20 billion to keep the B52s flying until the new bomber is ready for duty.

An updated B1 could be flying in 1986 or 1987, under advertised timetables subject to change, and the Stealth in 1988 or 1989. Skeptics predict that Stealth would not be ready until well into the 1990s, given all the technical "unk-unks" -- the term for unknown unknowns.

Among the other arguments the two-bomber advocates are putting forward against the Stealth-only approach:

Stealth would not be as suitable as the B1 for carrying conventional bombs around the Persian Gulf or for bearing nuclear-tipped cruise missiles aimed at the Soviet Union. This is because the Stealth bomber on the drawing board is smaller than the B1 -- deliberatley so, to make it harder for enemy radars to detect.

A combination of B1 and Stealth bombers would enable the Air Force to build Stealth expressly for radar evasion rather than forcing designers to undercut those features by rigging the penetrator with gear to carry iton bombs and cruise missiles.

But Weinberger has severe budget problems that make the one-bomber approach look tempting, especially since the big bills for Stealth would not come in for a few years, leaving more money to pay for all those new weapons President Reagan has ordered to "rearm America."

"Something has to give, and Weinberger knows it," said one veteran staffer on a congressional military committee. "The political campaign is over. Now he has to find a way to pay for all this stuff, and can't."

The military services are embarked on their biggest weapons-buying spree since World War II. Even the $1.5 trillion Reagan has requested for the next five years cannot finance everything on their shopping list, according to specialists at the OMB and in Congress.

For example, the House Armed Services Committee, historically the Pentagon's strongest congressional ally, has concluded that Reagan cannot possibly pay for all the ships he has promised to buy the Navy. It would take $17 billion to $20 billion in fiscal 1983 alone to finance the ships Reagan has ordered, the committee said.

The big-ticket items are the $3 billion Nimitz aircraft carrier, the $3 billion CG47 Aegis Cruiser and the $2 billion Trident missile submarine.

The fiscal 1983 shipbuilding cost, unless Weinberger cuts it, will be twice the $10 billion earmarked for fiscal 1982, already a peacetime record. "He's going to have to cut or stretch out something," said another congressional ally of the Pentagon.

If that something turns out to be the B1 the Air Force wants, the Reagan administration lays itself open to the charge that it did just what the Republican Party assailed Carter for doing.

Another option is to deploy a less elaborate MX missile offense than the Air Force advocates. That decision is further away than the one on the bomber, probably early July. The challenge is to find a place to put the missile where the neighbors will accept it.