Defense Secretary Harold Brown yesterday defended President Carter's veto of the $38 billion weapons bill as necessary to reverse the trend toward larger, but fewer, ships.

"We need to have the strongest Navy. I think we do have the strongest Navy," Brown said. But "I think we can continue to do so only if we reverse the trend toward smaller and smaller numbers of larger and larger, more expensive ships."

Carter vetoed the weapons bill Thursday primarily because he objected to a $2 billion nuclear-powered aircraft carrier included in the funding. He said the money could be better spent on other military projects.

Brown agreed yesterday with Carter's conclusion, noting that the nuclear carrier diverted "funds for readiness, for repairing existing ships, for allowing more steaming time . . . for Army ammunition and so no."

"Add those up, $2 billion, and you would see that a great deal has been cut out of our combat capability," Brown said.

"What the [Carter] objects to, and I object to, is the substitution of an expensive nuclear aircraft carrier for other things more urgently needed for our defense."

Brown was questioned on the television program "Issues and Answers" (ABC, WJLA).

Noting the expansion of Soviet military forces, he said, "Having strong nonnuclear forces in general, including naval forces, is extremely important to avoid having to threaten escalation to nuclear war."