The nation's retailers lost $1.8 billion last year to theft and errors, including shoplifters, whose top light-finger item was ladies' designer apparel, according to a survey.

"An Ounce of Prevention," the 10th annual survey of U.S. retailers by the Arthur Young & Co. accounting firm, said this week that jewelry, shoes and men's clothing were at the bottom of the list."Our survey shows that many of the nation's retailers have been hit hard by theft and other losses," said Gerald Smith, head of Arthur Young's retail group in Chicago, a management consultant for the retail industry.

The survey found companies lost $1.8 billion through shoplifting, theft by employees or vendors and errors in paperwork in 1987, compared with $1.5 billion in losses in 1986.

The survey covered 119 retail companies operating in 47,000 locations around the country with combined total sales of $127.5 billion, Smith said. The research was conducted last spring and summer.

Companies participating in the survey included discount stores, department stores and specialty stores. The names of the firms were withheld.

Discount stores were hit hardest last year, losing $1.2 billion worth of merchandise; department stores lost $364 million and specialty shops lost $233 million worth of goods, the survey said.

For the five years from 1982 through 1987, the survey found the following increases in shoplifting losses as a percentage of total sales:

-Discount stores: from 1.5 percent to 2.1 percent.

-Specialty stores: from 1.7 percent to 2.2 percent.

-Department stores: from 2 percent to 2.1 percent.