The Navy's F18 fighter comes under fresh fire in Congress today, with the Senate scheduled to vote on an amendment that would cancel the whole multibillion-dollar project.

Sen. Gary Hart (D-Colo.) is scheduled to propose the amendment in the second day of debate on a bill authorizing the Pentagon to spend $36 billion for weapons in fiscal 1979. Hart said yesterday that $15 billion could ultimately be saved by shooting down the F18 now.

His amendment is expected to be the most controversial of those offered, partly because of the F18's wide political backing. But Senate vote-countens said yesterday the plane is likely to survive the challenge by a comfortable margin.

Hart argued in a letter to colleagues yesterday that building the F18 woold keep the Navy from switching to small carriers with planes that could take off and land on a short stretch of deck. He said the $2 billion Nimitz-class nuclear carriers are becoming increasingly vulnerable to Soviet weapons, such as antiship cruise missiles.

"If the Navy is to survive in the face of the Soviet anticarrier threat," Hart said, "we must acquire as large number of smaller aircraft carriers" that can be dispersed around the world.

Besides slowing the Navy's switch to small carriers with V/STOL (vertical and short takeoff and landing) aircraft, Hart said, the F18 would give today's big carriers less protection than the F14 fighters the new plane would partially replace.

The senator noted that the F14 carries six Phoenix missiles that could simultaneously take on six antiship missles headed for the carrier, while the F18 could combat only one of them. Hart termed antiship missles "the main threat to the aircraft carrier."

Although the F18 was supposed to be a lower-cost alternative to the F14, Hart said that "according to Navy information" the F18 will cost $25.4 million each in the fiscal 1979-83 period compared to $22.8 million for the F14.

The Carter administration split over whether to continue developing the F18 when it drafted the fiscal 1979 defense budget. Navy Secretary W. Graham Claytor recommended canceling the F17 and buying instead more A7 attack planes for the Navy's bombing needs and more F14 fighters for air defense.

Political support for the F17 goes beyond the congressional delegations from the states of the principal contractors, Northrop Corp. of California and McDonnell-Douglas of Missouri. House Speaker Thomas P. (Tip) O'Neill Jr. also has taken a fervent interest in the F18, which would use General Electric engines built in his home state of Massachusetts.

The Pentagon currently plans to buy both fighter and attack versions of the F18. The F18 fighters would be mixed in with F14s on carrier decks, while the attack version would replace the A7 attack plane.

The F14, built by Grumman on Long Island, and the A7, by Vought Corp. of Dallas, are being championed by the New York and Texas congressional delegations.

0190 - Add three procurement TTS

The Senate Armed Services Committee in its report on the $36 billion bill said the F18 and F14 "are complementary, not competitive." The committee recommended raising the administration's request for the F18 fighter and attack programs from $311.9 million to $429.5 million.

As of last night, there was no amendment in sight to take out $1.9 billion the Senate committee added to the Pentagon budget to buy another Nimitz-class nuclear aircraft carrier - which President Carter does not want.Administration officials passed the word to their Senate allies yesterday that they would make their stand against the Nimitz when the appropriations bills for the Pentagon are voted on later.

Armed Services Chairman John C. Stennis (D-Miss.), said in operning the debate yesterday, the services are straining to fill their ranks with volunteers, adding that "that time has come to consider our alternatives."