The Air Force yesterday made its biggest financial commitment to a small, mobile land missile by awarding contracts totaling $447.6 million to Martin Marietta Aerospace Corp. of Denver to assemble and flight-test the "Midgetman."

Under the current Air Force concept, the 46-foot-long, single-warhead rocket would be towed between military bases, making it difficult for attackers to target. The Martin Marietta subsidiary will assemble the three-stage missile and flight-test it at Vandenberg Air Force Base north of Los Angeles.

The Air Force contracts will run at least five years, with a three-year extension possible. The first flight test is scheduled for 1988, the Air Force said, with deployment in the early 1990s.

Yesterday's award comes against a backdrop of technical progress and political controversy over the Midgetman. While off to a fast start, the missile's fate is uncertain because of political and military developments beyond the Air Force's control.

At White Sands Missile Range, N.M., last week, scaled-down models of vehicles that would haul the missile were subjected to a simulated blast from a nuclear warhead. The Air Force said the blast was equivalent to 1 megaton on a full-sized vehicle. The Midgetman carriers withstood the blast with little or no movement, the Air Force said.

The test results buoyed hopes of Air Force officials working on Midgetman, although they cautioned that readings from instruments attached to the vehicles have not yet been analyzed.

Midgetman supporters also received a boost last week from the House, which voted to authorize $150 million above President Reagan's request for the missile's research and development.

The Senate voted the $624.5 million Reagan requested for Midgetman -- $515.4 million for the missile and $109.1 million for the vehicle.

Yesterday, a number of senators were mapping a campaign to wipe out the additional $150 million on the ground that there are still too many unanswered questions about Midgetman, such as its final cost and its ability to survive if the United States and the Soviet Union do not reach agreement on limiting the number of warheads in their arsenals.

The political battle over Midgetman will be joined next week at a House-Senate conference on rival defense authorization bills.