Prices of personal computers and related equipment vary widely at stores in the Washington area, and some of the lowest prices are to be found at stores rated high for service, according to a survey to be published today by Washington Consumers' Checkbook magazine.

Comparison shopping at 44 stores, the magazine found variations of several hundred dollars on identical items. In addition, the magazine found, some stores offer extra equipment or service, such as installation, as part of the quoted price, while others do not.

In an extensive report on the personal-computer boom, the magazine -- an independent, Washington-based monthly publication -- advises readers to consider carefully whether they really need a computer at all. "If you can't clearly see how you would use a personal computer for work or play, don't buy one," it suggests.

For those who do need a computer, Checkbook suggests, as Money Magazine also did in a recent similar report, that the decision on which one to buy should be made on a "software-first" basis. That is, the consumer should select the programs and functions that he or she needs, and then buy a machine that will handle them, rather than starting with the machine itself.

Once a decision to buy is made, Checkbook says, the cost can vary by several hundred dollars, depending on the store. For example, an Atari 800 computer was priced at $1,100 at Computer Age in Silver Spring and $1,696 at Computer Systems Consultants in Leesburg. The price of a Televideo 950 Terminal was $995 at Frederick Computer Products in Frederick and $1,250 at Micro Research Inc., Falls Church.

However, price is not the only determinant of value for dollar, the report says. Some stores include free or discounted software with the computers they sell, others don't, with the difference sometimes being several hundred dollars. Some install and test the equipment at the work site, others just sell it in boxes for the user to set up. And some include supplementary gear such as cables or detailed manuals, others do not.

In addition, the report says, the quoted prices are actually negotiable at many stores.

On the basis of price, quality of sales advice, and after-sale service, the three stores that drew the most favorable overall ratings were Frederick Computer Products, Clinton Computer Center in Clinton, and HLA Inc. in Beltsville.

"Several of the firms rated highest for service . . . also had low prices. This was particularly true of Clinton Computer Center and Frederick Computer Products," Checkbook says.

Some stores that offered relatively low prices on some items were above average price on others, the survey found. For example, at American Computer Center, 807 H St. NW, the price for the Atari 800 System was "12 percent above the area stores' average Atari 800 price, while American's price on the Diablo printer was 13 percent below the average."

The highest average prices for the items included in Checkbook's comparison shopping test were found at Entre Computer Center, McLean; Trico Business Equipment, Fairfax; and Virginia Micro Systems Inc., Woodbridge.

The lowest overall average prices were found at Geo-Computers, Columbia; Dagar Corp., 2138 P St. NW.; Frederick Computer; and Hi-Fi Buys, Springfield.

The equipment in the survey comprised two "low cost, consumer-oriented systems," the Atari 400 and the VIC 20; and five of the most popular middle-priced, middle-capacity systems, the Apple II Plus, Atari 800, Zenith Z-8981, Hewlett-Packard 85, and NEC PC-8000, as well as peripheral equipment such as printers and modems.

The Radio Shack chain, which features its own TRS 80, was not included in the survey because they generally carry their own equipment and their own software, not the variety of competing items found in other retail stores.