A fierce lobbying and propaganda battle between two military contractors could peak in the House as early as today with a vote to buy either Lockheed Corp. C5B Galaxies or modified Boeing Co. 747 wide-bodied airliners to expand the nation's capacity to airlift military equipment to world trouble spots.

The battle has been ferocious, mainly because it involves a Pentagon civilian and military leadership infuriated by Boeing's unprecedented decision to fight the Defense Department's choice of the C5B and because billions of dollars, thousands of jobs and the contractors' futures are at stake.

Torrents of claims and counterclaims have tumbled forth, particularly since the Senate voted in May to reject C5Bs in favor of used 747s. Most of the claims are bitterly and even contemptuously disputed, and many are technically mind-boggling and resistant to proof. Adversaries even dispute whether 48 or 55 new 747s could be the proposed substitute for a purchase of 50 C5Bs.

Here is a summary of the background and key issues:

The Air Force, saying "prepositioning" of equipment and specially built ships may be fatally slow for the Rapid Deployment Force, had wanted an all-new cargo aircraft, the C17, capable of carrying "outsize" items, such as CH47 combat helicopters, tanks and eight-inch self-propelled howitzers.

The House and Senate Armed Services and Appropriations committees, respectively, refused unanimously to fund C17 development. Congress then ordered the Pentagon to study strategic airlift needs, and the results, completed a year ago and largely classified, contain four "scenarios" for emergency airlifts.

At the heart of the controversy are the scenarios and the Air Force's 77 Galaxies, the world's only fleet capable of carrying outsize gear. These airplanes, called C5As, are highly controversial, partly because they eventually required new wings at a cost of $1.6 billion.

Early this year, the Pentagon told Congress it wanted to buy the 50 C5Bs and 44 KC10s, military versions of DC10 wide-bodied airliners. The KC10 manufacturer, McDonnell Douglas, had won a design competition for the C17. Galaxies, KC10s and 747s all can haul oversize equipment, such as trucks and jeeps and bulk cargo.

Boeing says the scenarios show that if the 77 existing Galaxies, after being rewinged, were to be used predominantly for outsize cargo, 48 747s could handle the remaining oversize and bulk equipment.

The Pentagon strongly disagrees, saying that within two weeks of mobilization, the 77 Galaxies could carry 40 percent to 90 percent of the outsize items, depending on the scenario. A Congressional Budget Office analysis supports the Pentagon.

The estimated cost differences are large but disputed. In 1982 dollars, the 50 C5Bs would cost $8.1 billion to acquire and $7.9 billion to operate and maintain for 20 years. Boeing's comparable figures for 48 used 747s total about $7 billion less.

But the Pentagon rejects Boeing's figures, saying that the correct number of 747s is 55, that they would be a mix of new and used planes and that the total life-cycle cost would be $15.1 billion, a relatively small $900 million under the 20-year figure for C5Bs.

Other highlights of the controversy:

* C5B advocates also say that it is inefficient and impractical for the aircraft to carry exclusively outsize cargo.

Some critics say, however, that the need for strategic airlift is overstated because experience has shown that much more time is needed to prepare troop units to move and load than to transport them, and that a mechanized division that can be moved by seven or eight of the special ships would require at least 800 C5B round-trips. The Soviet Union has no outsize airlift capability.

* Boeing says used 747s, which troubled airlines want to sell, could be quickly converted into freighters, providing a three-year delivery edge over C5Bs. Because the 747s are in production, Boeing's cost estimates are based on experience that the C5Bs lack, the Galaxy production line having been shut down for nine years.

* C5B advocates praise its ability to land on austere airstrips with runways 800 feet shorter than those needed by the 747 and the way in which equipment can be driven off it or loaded directly onto trucks.

Advocates of the 747 say that with an 80-ton payload, its range is 4,900 nautical miles, or 1,500 more than the C5B, and that its takeoff runway can be 800 feet shorter. They also note that its 135-ton capacity for other than outsize cargo exceeds that of the C5B by 35 tons, and that its fuel economy, speed, reliability and maintenance records are vastly superior.

Boeing guarantees no more than 20 man-hours of maintenance per flight hour, while Lockheed claims the C5B will need 40, compared with 74 on existing Galaxies.