Ten months after cartoonists and weapons-procurement reformers had great sport about the $640 custom-made toilet cover it built for a Navy plane, Lockheed Corp. is all the more convinced that it was unfairly pilloried.

The company, stung by what its corporate executives describe as a public-relations black eye, agreed in February to lower the price to $100 each for 54 of the toilet parts. Then, hoping to cap the controversy, the company invited 30 small plastics products firms to bid for the next lot of 10 covers.

The companies declined to bid because, with such small quantities required, "they knew they ain't going to make a buck," Lockheed spokesman Rich Stadler said yesterday.

"Our reason for going outside was to find out if there was a way to lower the price," he said. "The evidence we have shows we were offering a very fair price. If someone can do better, we'd be very happy for them to take over the job."

Lockheed, he said, will continue to supply covers to the Navy at the "lowest possible price" -- $544 each. The company's internal audits showed that the original $640.09 price tag was 15 percent too high, he said.

Two senators who had trumpeted the issue last February, amid growing congressional scrutiny of Defense Department procurement practices and offers by small companies to sell the covers for as little as $120 apiece, challenged Lockheed's conclusions yesterday and reiterated that the item is overpriced.

"It shows the inflexibility of large corporations to find good sources," Sen. William V. Roth Jr. (R-Del.) said. "I'm not convinced that they can't find a smaller company without high salaries and administrative costs to build these things cheaper."

Sen. William S. Cohen (R-Maine) said Lockeed's stated inability to make "a modest product for less than $600" means "the Pentagon may have to go in-house for its outhouse."

At issue is "toilet cover assembly 941673-101," as the Pentagon refers to it, a plastic and fiberglass shroud that fits over the lavatory holding tank in the P3 Orion submarine-hunting aircraft.

Lockheed had produced hundreds of the planes without controversy until the Navy ordered 54 toilet covers as spare parts last year.

Stadler said the covers are costly to reproduce in small quantities because the Navy prescribed 30 specifications, ranging from color (tan) to strength and fire resistance.

Pentagon critics cited the covers' price to dramatize their charge of runaway procurement costs. A newspaper cartoonist portrayed Defense Secretary Caspar W. Weinberger wearing a toilet seat around his neck. Attached to the seat was a $640 price tag.

H. David Crowther, Lockheed's vice president for communications, said the company was badly shaken by media reports suggesting that "we're dishonest, that we deliberately set out to cheat the Defense Department."

"The chairman of the board got letters from little old ladies in Nebraska, saying, 'Shame on you. You're unpatriotic.' Our employes were standing in supermarket lines, and their neighbors asked them if they had sold any toilet seats lately. All of that is painful," he said.

Lockheed decided in February to "policy price" the 54 covers at $100 apiece to "prevent this from becoming an unnecessary diversion" from larger defense issues, officials said at the time.

Bid invitations were sent in July to 30 firms specializing in plastic products. Included was Sperzel Industries of Nevada, Mo., whose president, Richard Strau, had earlier been quoted as saying he could produce the part for $15.

Strau could not be reached yesterday.

One firm overlooked in the bidding process is Capital Plastics Co. of Kensington, which told Senate aides earlier this year that it could have produced 54 of the covers for $120 each. Tim Sullivan, company vice president, said yesterday that Lockheed skewed the bid by limiting the quantity to 10.

If the order was larger, he said, "I'd like a shot at it. Give me the seat, and let me do it. All I need is 120 bucks."