This may seem confusing, but it isn't, as you will see, even though it's about a very expensive idea that flew and yet hasn't flown.

The idea is called the Helistat, an ingenious contraption in which large amounts of federal dollars are being invested and about which every expert except its sponsors is screaming bloody murder.

The Helistat, now being assembled in a big hangar at Lakehurst, N.J., is being ballyhooed by the U.S. Forest Service as the wave of the future in forest management, a 343-foot-long helium blimp with four helicopters attached.

If and when it flies, the Helistat would go out over remote, roadless sections of forests, lift out 25 tons of timber and carry it as far as five miles back to a loading point.

In weight and distance, that's about five times better than today's single logging helicopter can perform.

"Our interest in it," said George Leonard, timber management chief at the Forest Service, "is that it appears to offer an opportunity to remove logs from areas where it is economically or environmentally unwise to put roads . . . . We are trying to demonstrate that the concept is feasible." So far, so good. But it's here that the story about the Forest Service's elephantine pet takes a magical turn.

The General Accounting Office (GAO) says it's a boondoggle. The Federal Aviation Administration questions the builder's workmanship. The Navy and the National Aeronautics and Space Administration officials worry openly about its design.

A GAO report in November said the Helistat's original estimated net cost has escalated from $6.7 million to at least $31.7 million, it is far off schedule and its technical problems are so great that the big beast may never fly.

And when Rep. Sidney R. Yates (D-Ill.), taking all this into account, tried to cut $2.6 million from the Helistat's $4.6 million budget for fiscal 1983, the House Appropriations subcommittee that he chairs rolled right over him and restored the money.

Rep. John P. Murtha (D-Pa.), sponsoring the amendment to restore the money, told Yates that the Navy's serious concerns were simply not to be trusted. Funny thing, said Rep. Silvio O. Conte (R-Mass.), this is the same John Murtha who takes Navy word as gospel when it wants more money for itself.

The project is a brainstorm of Frank Piasecki, a recognized pioneer in helicopter development, who heads Piasecki Aircraft Corp. in Philadelphia. He proposed that the Forest Service find some federal money to help him build it.

"We had no money, so the idea had to be sold on the Hill," Leonard said. The Forest Service intends to recoup some of the investment by marketing timber that the Helistat would haul in demonstration flights.

The foresters went to Robert B. Duncan, a former congressman from Oregon and member of the Appropriations Committee, who took the idea and flew, er, ran, with it. He got $3 million earmarked for Helistat in 1979.

"I had some confidence in it and I still do," Duncan said last week. "But this is an effort to see if the concept will work. It's not intended to be a prototype and I think the GAO is critical because it is not . . . . Frank is no nut. He is trying to prove a philosophy and he is trying to do it on a shoestring."

The shoestring, actually a $10.7 million contract, is being pulled from several angles, it appears. Duncan, now practicing law here, continues to work on the Helistat. "I told Frank I couldn't work on it without getting paid, so I've sent him a couple little bills in the last few months. I've got to eat, you know."

Also helping on the sidelines is Duncan's former staff assistant, David L. Burt, now in the consulting business, who was hired by Piasecki to be his eyes and ears in Washington.

"GAO generally does a good job," Burt said, "but I think this criticism is unwarranted. A lot of people think this is a daring idea . . . . It's a shame that it's being criticized so unfairly."

The latest GAO report--the second critical blast in two years--said that "the lack of user support, coupled with the dramatic increase in program cost, makes the continuation of the program questionable."

The 1981 GAO study reported that potential users saw little practical application for a vehicle like the Helistat. The new report raises questions about the cost overruns and concerns about the craft's structural integrity.

GAO has given Agriculture Secretary John R. Block until mid-January to answer a series of questions about the project. Meanwhile, Piasecki is planning preliminary tests of the Helistat in the spring and flight tests in the summer.

"It's not a boondoggle," Burt said. "We're going to prove the GAO wrong. The criticism is premature. It is going to be a tremendous project."

The tests will be conducted at Lakehurst. It was there, incidentally, that the largest rigid airship ever built, the Hindenburg, crashed in flames in 1937, killing 36 of its 97 passengers.