President Carter unveiled his five-year shipbuilding plan for the Navy yesterday, a program so austere that it seems certain to send much of Congress to battle stations.

The Carter program features fixing up existing ships to make them last longer and a shift toward construction of less expensive aircraft carriers than today's nuclear giants of the Nimitz class.

"This is an adequate and realistic plan," Defense Secretary Harold Brown wrote House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) in sending to Congress the shipbuilding plan for the five-year period fiscal 1979 through 1983.

However, the Carter administration plan would provide only about half as many new ships as Navy leaders had sought, 70 instead of the 156 envisioned under the five-year plan developed in the last year of the Ford administration.

At one time, Navy leaders were pushing for an 800-ship fleet but lowered that target in recent years to a 600-ship Navy. Brown wrote Congress that the Carter program would "increase the fleet size from about 465 ships at the end of this fiscal year to over 525 ships by end of fiscal year 1984."

The Ford administration five-year plan would have cost about $49 billion while the stripped-down Carter version is expected to total about $28 billion.

The Carter program calling for the construction of 70 ships and the modernization of 13 existing ones includes no money for another Nimitz-class nuclear aircraft carrier. Instead, it recommends building a medium-sized, nonnuclear carrier starting in fiscal 1980.

The House Armed Services Committee already has informed the House Budget Committee that it intends to authorize money this year to build another Nimitz-class carrier and nuclear cruiser, even though the Carter administration does not want them.

Senate military committees are also expected to add more money for Navy shipbuilding than the president is requesting.

The blueprint for the future Navy thus is expected to be smudged by a series of battles between the administration and Congress.

Said Secretary Brown of the five-year shipbuilding plan: "When added to the ships already authorized but not yet delivered, it will yield a growing naval force in the mid-1980s which I believe will be adequate to cope with the Soviet navy as we now envisage Soviet capabilities to be in that period . . ."

These are the elements of the 83 ship plan for fiscal 1979 through 1983.

New surface warships - One conventionally powered carrier to be funded in fiscal 1980; one nuclera cruiser funded in fiscal 1983; seven DDG47 destroyers; 26 FFG7 patrol frigates.

Modernization of surface warships - Two Forrestal-class carriers; 10 DDG2 destroyers.

Nuclear submaries - Six Trident missile boats and five SSN688 attack subs.

Amphibious ships - One LSD41 to be funded in fiscal 1981 and second in fiscal 1983. The Marine Corps sought more.

Antisubmarie and support ships - 12 TAG OS ocean surveillance ships; one destroyer tender; five mine countermeasure ships; one oiler; two seagoing tugs; one cable repair ship, and one converted cargo ship.

Brown told Congress he delayed submitting yesterday's five-year ship building plan until the Navy had finished its broad study of what kind of fleet it should build for the future.

That study is now finished. The most austere of the options presented, sources said yesterday, is more ambitious than the five-year plan adopted by the Carter administration.

The sharply slashed Navy shipbuilding program comes on top of strategy guidance from Pentagon civilian leaders calling for what Navy leaders regard as a secondary role for their service. Adm. Elmo R. Zumwalt, former chief of naval operations, said in an interview with The Washington Post that he had read the guidance "and it belongs in the funny papers."