Polaroid Corp. today announced plans to lay off 800 workers, most in the camera division, in a belt-tightening measure triggered by a first quarter sales slowdown and a severe inventory build up.

"We feel we have no alernative during this unsettling economic period," wrote company president William J. McCune Jr. in a memorandum ordering production cutbacks, a ban on overtime and a reassignment of personnel.

The layoffs come after disappointing first quarter sales-up 10 percent to $264.9 million though below projections-attributed to continued inflation and energy problems.

McCune conceded the company's heady 28 percent boom in earnings and soaring sales last year caused a miscalculation in sales projections for 1979, resulting in excess inventory predominatly in cameras.

"Basically we're dealing with a lousy economy," said company spokesman Donald Derry. "In late December we began to detect a very rapid transfer from a boom to a slowdown; we made adjustments along the way but the economy has gotten softer than we thought it was going to get."

While the company is now "optimistically cautious" about 1979, it is planning for a sales growth with the possibility of an improved sales environment for the second half of the year, Derry said.

Some market analysts, however, are raising the red flag for Polaaroid's future, urging extreme caution in near term purchases.

"The situation for Polaroid is extraordinarily dire," said Brenda Lee Landry, a vice president with Merrill Lynch. "Instant film camera sales are a disaster with dramatic declines in domestic sales."

The "One Step," the best selling instant camera in the nation, as well as the firm's SX-70 film have received a sour response on the marketplace over the first four months of the year, she says.

"Last year they were back ordered for one million units of the "One Step," said Landry. "This year they're having a hard time giving them away."

She predicted: "It will be a very tough year and by the second quarter it will be very, very, very rough."

Another Wall Street analyst and veteran Polaroid observer agreed, "The near term environment is extremely uncertain and very unpredictable; I view the second quarter as a pretty flat quarter."

However, he added: "Polaroid is still a good solid company and I feel confident it will pull itself out over the long run.

"Camera sales won't fall out of bed," he observed.

He said Polaroids layoffs, to be accomplished over the next two weeks at the Norwood, Mass., facility, and other economic measures imposed today are actually an indication of McCune's stronger management role in the company-"a good sign for the firm's economic future."

But Merrill Lynch's Landry pointed pessimistically at what she claims is a further sign of the company's economic decline, Polaroid's decision to borrow to support working capital needs for the first time in 20 years.

She added, "Since mid March we have been telling our customers that Polaroid's domestic sales are in very serious trouble."