The Pentagon is not expected to cancel the F18 this year despite findings by Navy test pilots that the attack version of the plane did not achieve the range required for anti-ship missions.

Navy leaders said in interviews recently that they will concentrate instead, at least for now, on providing more fuel for the twin-jet F18 so it can travel farther.

When the F18 flunked part of its combat test over the Pacific, the biggest single shortcoming was its failure to make a 550-mile round trip carrying a bomb load, Navy leaders said.

The Pentagon has said it will buy as many as 1,366 fighter and attack versions of the F18 for the Navy and Marine Corps under a $40 billion program. But whether the program just getting under way should be completed is expected to be argued fiercely in Congress' lame-duck session that starts in two weeks and next year when the Pentagon's fiscal 1984 budget is submitted.

To help extend the F18's range, a top Navy official said his service will do "something different on the tanking." That means either larger fuel tanks or more flying tankers assigned to mid-air refueling. Attaching larger tanks to provide extra range is often done but can mean more drag and less maneuverability.

Aerial refueling of the F18, officials said, could be done by A6 tankers flying from aircraft carriers or through the "buddy system." The latter consists of one F18 transferring fuel to another from an oversize fuel tank.

It would be ironic if A6 tankers ended up saving the F18 from cancellation. Grumman Aerospace Corp. of Bethpage, L.I., would like to see the Navy buy its A6 light bomber as an alternative to the troubled F18. The F18 is manufactured by McDonnell Douglas Corp. of St. Louis and Northrop Corp. of Century City, Calif.

The Navy pilots' report on F18 flaws also increases the likelihood that House Armed Services Committee Chairman Melvin Price (D-Ill.) and House Appropriations defense subcommittee Chairman Joseph P. Addabbo (D-N.Y.) will square off in the debate on whether the progam should be continued.

Some McDonnell Douglas workers live in Price's district and Grumman employes in Addabbo's.

Backers of the F18 insist that improvements are in the works. They also note that the range of an airplane depends in part on how and where it is flown.

A pilot who touches off the engine's after-burner for more thrust is like an auto driver who floors the accelerator. The engine gulps fuel in both instances.

A plane dashing in low toward a ship to escape radar detection and anti-aircraft fire also burns more fuel than one cruising toward a target at high altitude, thus reducing its combat radius unless refueled in mid-air.

The next big Pentagon review of the F18's future is scheduled Nov. 30. The last confrontation -- over the plane's cost--ended with McDonnell Douglas agreeing to a price of $22.5 million in the fiscal 1982 order.

"We're going to be fighting the battle of the F18 every year," conceded one Navy executive who favors buying the plane at least through fiscal 1984.

In the end, Congress -- if not Navy leaders and Pentagon civilians -- could decide the surer course would be to buy a mixture of Grumman F14 fighters and A6 bombers rather than the full order of the attack version of the F18.

The F18 is designed to serve as a light bomber and dogfighter. The plane's future as a dogfighter is not under as much challenge as its attack role. Of the planned buy of 1,366 F18s, 1,059 were envisioned for the attack role and the rest for aerial dogfighting, reconnaissance and tactical air control.

Its backers stress that a pilot flying an F18 loaded with bombs for the attack mission can transform the plane instantly into a dogfighter by dumping its munitions.

"We knew we would have to accept some compromises to get a plane which could do both jobs," a top Navy official said. He added that the Navy pilots' findings that the F18 was short of the desired range for sea warfare missions did not come as a big surprise to Navy Secretary John F. Lehman Jr. and other top officials.