The telephones at the Better Business Bureau of Metropolitan Washington ring at least 500 times a day, every working day of the year. And there are only 480 minutes in an eight-hour day.

Most callers either want to register a complaint or are seeking information on an offer. The Bbb has tallied an impressive track record seeking redress for unhappy customers in and around the city.

Last year the bureau fielded around 115,000 phone calls from consumers, businesses and cautious investors seeking information on a wide range of deals, propositions and, unfortunately, rip-offs. Over 62,000 of the calls were requests for information concerning locally operated businesses and non-profit organizations. Each year the number of Better Business callers increases.

Calls are logged, classified, examined and finally categorized. For the BBB's statistics, two categories suffice -- the "top 10" for complaints and the same for inquiries.

The most prevalent complaint last year, according to figures published in the bureau bulletin, involved mail-order companies. Not included in that classification, but very high on the list of offenders, were photo processing firms, ranked third, and magazines ordered by mail, ranked fourth.

Filling out the top five complaints for 1979 were franchised auto dealers, taking second, and fifth-place auto repairs, excluding transmission repairs.

The top 10 in order: dry cleaning/laundries, department stores, travel agencies (including public transportation that arranges group tours), home furnishing companies, and music/record stores.

In addition to just compiling complaint statistics, the bureau attempts to redress consumer grievances and has a surprising success rate.For the top 10, the settlement rates range from a low of 53.7 percent for mail-order companies to a high of 90.8 percent for travel agencies. Other classifications showing a high degree of cooperation with dissatisfied customers after a call from the bureau include department stores (87.5 percent), home furnishing (81.8 percent) and music/record stores (87.2 percent).

Most calls to the bureau involve requests for information before a consumer has invested or bought. Just as customers seek bureau information, some companies try to put their best foot forward with the bureau, in hopes of creating a favorable resume for disbursal of inquiries.

Inquiry classifications, not surprisingly, include several of those that appear in the complaint category. Leading the pack were waterproofing companies, garnering 1,532 report requests. Following closely were "other home improvement companies" (1,502 reports), home remodeling companies (1,457) and roofing contractors (1,293).

The 1979 list dropped sharply after the home repair concerns, picking up with franchised auto dealers (863), moving and storage companies (814) and auto repairs shops (788). The inquiry category top 10 were completed by report requests for mail order companies (783), insurance companies (774) and, finally, heating and air conditioning companies (671).

Nationwide, the 147 Better Business Bureaus fielded over 7.4 million consumer service requests. A primary reason for the huge number of calls, according to BBB sources, was that "many consumers recognized the BBB as as a source of information which could help protect their shrinking dollars during these inflationary times."