Navy leaders have won a key round in their fight to build a new generation of aircraft carrrier planes that can take off and land vertically.

They have persuaded Defense Secretary Harold Brown, Pentagon sources said yesterday, to restore the deep cuts he had tentatively made in the Navy fiscal year 1979 and 1980 budgets for these aircraft.

If the cuts had remained, Navy official said, the opponents of switching from giant Nimitz-class carriers to smaller and cheaper ones would have had a stronger argument than ever.

Why go ahead with the unproved medium-sized carrier, opponents would argue, when the Defense Secretary himself has slowed the Navy program to build the planes tailored for the smaller ship?

Navy Secretary W. Graham Claytor, Pentagon sources said, told Brown in appealing the cuts that the House Armed Services Committee would make that argument most vigorously. The majority on that committee wants to stick with the Nimitz-class carrier.

Specifically, in his first review of the Navy's five-year money plan. Brown cut $29 million from the $96 million requested for the aircraft in fiscal 1979 and $56 million from the $167 million requested for fiscal 1980, sources said.

Brown, after hearing appeals from Claytor and Adm. James L. Holloway, chief of naval operations, restored the cuts for both those years but slashed the Navy requests for V/STOL (vertical and short takeoff and landing) aircraft development work in later years.

Navy leaders are not worrying about those more distant cuts, figuring that their progress on V/STOL over the next two years will win more generous financing for fiscal years 1981 through 1983.

The less space a plane needs to take off, the smaller the aircraft carrier can be. Claytor and Holloway contend that the Navy could build two medium-sized carriers for the price of one $2 billion Nimitz and cover more of the world.

Opponents counter that neither the medium cartier nor the V/STOL planes to go aboard it is a proven concept from cost and operational standpoints.

Brown not only has doubts about the Navy's proposed $1.2 billion V-STOL airplane plan as well. The Marines want to buy a version designated the AV-8B, but Brown has yet to approve their plan for the next five years.