Boston — Secondhand has become respectable. The nation is altering its conviction that ''used'' is second best and is taking a new look at secondhand goods, according to economists and merchants.
From clothes to cars, Americans are now seeking out or settling for the low prices and proved quality of used goods. The change in image has even led to a change in name: used is no longer used, it is now ''pre-owned.''
Secondhand sales have spread from thrift shops and tag sales to the mainstream of the economy:
* Steve O'Hara wants to go national with his used-car marketing company, Detroit II. He has eight dealerships operating in central Florida and hopes to have 4,000 to 6,000 in operation by 1987. His plan is to take the onus of unreliability off used cars by stamping the brand name ''Detroit II'' on them and guaranteeing their quality.
* In California's Silicon Valley, shoppers browse for a different kind of bargain: used computer parts. Halted, a store that specializes in everything from oscilloscopes to microprocessors, had earnings last year of more than $1 million.
* Uncle Sam has become a major supplier of used goods to public and private institutions. Everything from desks to space capsules are being snatched up by local governments and nonprofit organizations. Last year the federal government distributed $349 million worth of surplus property at a fraction of its original cost.
Growing sales of used goods aren't limited to exotic merchandise. Increases are reported in sales of used bicycles, cameras, furniture, and televisions. Even used clothes - perennially relegated to thrift shops and tag sales - have become ''vintage apparel'' in some quarters.
Overall statistics on used goods are a rare commodity, but it is possible to trace the growth of sales in terms of individual items. For instance, used car sales climbed to a record 18.8 million in 1980, according to a study by Hertz. The figure dipped slightly in 1979, though the decline is attributed to the lack of additional used cars rather than the lack of demand.
The trend toward secondhand buying is also evident in the growth of the auctioneering business, especially industrial auctions. Irving Rabin, a partner in the San Francisco firm of Rabin Brothers Auctioneers, reports that corporate buyers are flocking to auctions because of low prices, instant delivery, and the availability of spare parts or accessories to go with the equipment.
His firm recently conducted an auction that included over 10,000 pieces of large machinery from the Great Atlantic & Pacific Tea Company facility at Horseheads, N.Y., an auction that lasted five days.
Mr. Rabin says attendance at auctions has risen 20 percent in the last two years. ''Business is very good. There's definitely a change in the type of customers we're seeing. It used to be you wouldn't see many major firms at these auctions. Now every major firm in the country and the world attends - and buys.''
He says contrary to popular belief, the auction business does not boom in recessionary times because few companies have excess cash for new equipment - be it new or used.
The reason for the surge in secondhand sales appears to be a matter of choice on the one hand and economics on the other. Some economists say it is simple - years of inflation have eroded Americans' buying power and forced many to cut corners wherever possible.
Other economists say they believe the growth in sales of used goods heralds a significant switch in consumer tastes.
''People are attaching less significance to everything being new,'' says Sandra Helmick, associate professor of family economics and management at the University of Missouri.
''We're moving away from a throwaway society to a greater acceptance of -secondhand goods,'' she says. ''And people are just plain settling for a lower standard of living when economics forces them to do so.''