They want to sell you a line.

About a dozen phone companies will soon begin a barrage of advertising as they intensify their campaign to win the long-distance business of Washington-area telephone users.

As this competition moves gradually through the area telephone exchange by telephone exchange, local consumers will begin to reap the benefits of "equal access," which makes dialing long distance on an alternative service as easy as calling on AT&T. Phone companies will enter into what the industry calls its "presubscription period," when customers may choose a long-distance service or, by doing nothing, elect to be randomly assigned to one.

In the blizzard of brochures will be advertisements for the "MCI Execunet" rate, the "SBS Skyline 1+ plan," the "Allnet-Alldialer" service, the "NetworkPlus ExpressLine" and "AT&T's Reach Out America" rate.

Just when you think you've got those straight, brace yourself for more letters touting the "Sprint Edge" or the "U.S. Tel Homeline," which of course is different than the "U.S. Tel All America 6."

With the advent of easier access to alternative long-distance telephone service in this area, phone companies are aggressively fighting for easier access to consumers' pocketbooks. At stake in Maryland, Virginia and the District of Columbia is a long-distance market worth an estimated $2 billion.

Special features being offered long-distance customers include discounts on calls placed when you travel, which vary widely from company to company, and bonus, volume and time-of-day discounts.

"Of all the changes that have swept through our phone system, none is so profound as the expansion of your operations for long-distance calling," say the authors of Washington Consumers' Checkbook's long-distance telephone survey.

"Equal access," mandated by the breakup of the Bell System, will give alternative long-distance companies the same services from the local phone company as AT&T has had, so that customers will get the same quality of connection they get with AT&T rather than hearing an echo or "fuzzy" sound when they use a competitor's service.

The process also eliminates the lengthy codes consumers previously had to dial to use the long-distance systems of AT&T's competitors.

Customers won't be required to replace equipment because the service will work on both rotary and push-button phones. No charges will be made for the switch to an alternative service.

A federal court has ordered that the services and connections of alternative services be equalized to AT&T in most of the country's exchanges by September 1986. Local Bell operating companies began switching to equal access a few exchanges at a time in July 1984.

In the Washington area, equal access already is available in the District in parts of Southwest and downtown; in Virginia in parts of Springfield, Alexandria, Herndon, Columbia Pike, Vienna and Arlington, and in Maryland in parts of Bethesda, Wildwood, Hyattsville and Gaithersburg.

The date that a consumer receives equal-access service depends on the first three digits (the "prefix") of his telephone number (see chart below). By Sept. 1, equal access will be available to 44 percent of all telephone lines in the District, 38 percent in Maryland and 50 percent in Virginia.

Bell Atlantic Corp., the parent of Chesapeake & Potomac Telephone Co., which serves the Washington region, said it will send a ballot to the majority of its millions of telephone subscribers in September, requiring them to "vote" for a primary long-distance carrier.

The primary carrier is the long-distance company that completes all long-distance calls a person makes from his home by dialing the area code and number. Customers can use other long-distance companies as "secondary carriers" by dialing "10" plus a 3-digit code, and then dialing the desired area code and phone number.

Consumers who don't choose a long-distance service about seven months after the initial mailing will be assigned to one of the long-distance carriers -- American Telephone & Telegraph or its competitors -- based on the ratio of votes each company received from customers who did choose.

That is, if one-third of the subscribers sending in ballots in an area prefer Sprint, one-third prefer AT&T and one-third prefer MCI, subscribers who don't vote have an equal chance of being assigned to one of the three.

The assignments will be made regardless of whether 3 percent or 95 percent of the subscribers respond to the mailing.

About 12 percent of the nation now has equal access. According to AT&T figures, roughly half the subscribers are voting for a serivce in equal-access areas, and nearly two-thirds of them choose AT&T. MCI says it is getting more than 20 percent of the vote.

Janis Langley, a spokeswoman for Bell Atlantic, said that under the assignment method, customers will receive a ballot three months before equal-access service is available to their line.

Those who do not choose within 40 days will receive a second notice assigning them to a long-distance company.

Customers then will have three to four months to switch to another long-distance service free of charge, Langley said. After that time, there will be a $5 fee for switching.

In addition to AT&T, consumers here can choose from five other "common carriers" -- GTE Sprint, ITT, MCI, Satellite Business Systems (SBS) and Western Union -- and a number of "resellers": Allnet, U.S. Telecom, TeleMarketing Communications, TDX Systems Inc. (for business only), NetworkPlus Corp. and TeleSaver.

Resellers are long-distance phone companies that rent time at a bulk discount on the transmissions facilities of a common carrier (such as MCI or AT&T) and then charge consumers for transmitting their calls over these facilities.

Researchers who have closely examined all of the long-distance services that will be offered here agree on one point: There is no overall "best" long-distance company.

Choosing a long-distance service is a complex process because the rates vary, depending on the time of day, location and length of call.

Everyone has different calling patterns, so one of the best approaches for consumers is to analyze a sample of past long-distance bills, according to Washington Consumers' Checkbook, one of several groups that has rated the quality and prices of local services.

Consumers' Checkbook has a computerized system that will evaluate phone bills for consumers and businesses for a variable fee. But, for those who want to compare services themselves, the U.S. Public Interest Research Group (U.S. PIRG) recommends finding a city that you call often and estimating the average length of your calls to that city and the time of day you make those calls.

PIRG then suggests comparing the cost of the calls among the different companies using a rate chart it has just published, which is available for $1.

For example, PIRG has calculated that if you have relatives in Boston whom you usually call on Sunday afternoons and you speak for about 15 minutes, it will cost you $2.46 with AT&T, $2.25 with SBS and $2 with Telesaver.

If this process is repeated for a few cities, PIRG says the consumer should be able to select the company that will provide the lowest-cost service to the cities called most.

The next step in choosing a long-distance service is to identify the special services you use. For example, note whether you make calls requiring services such as operator assistance, credit cards, collect calls, third-number dialing and dialing assistance. Then compare the services offered by the long-distance companies operating in this area and the charges.

"The differences in these services can sometimes drastically affect your long-distance bill," said Pamela Gilbert, co-author of the PIRG study.

Several Washington organizations provide charts comparing the services offered by each company. However, features and prices listed are subject to change frequently.

Tele-Consumer Hotline, jointly sponsored by Telecommunications Research and Action Center (TRAC) and the Consumer Federation of America, distributes a "Residential Long-Distance Comparison Chart" and various fact sheets.

TRAC also publishes its own long-distance comparison chart, available for $1, and will provide consumers with a personalized, computerized comparison of their rates for a fee.

Consumers' Checkbook, in its booklet on lower phone costs, provides several chapters on long-distance choices, features, rates, service quality and billing.

Among differences the booklet lists: A few long-distance companies impose monthly flat fees, regardless of usage. These fees are generally in the $5 to $10 range.

And some plans require consumers to pay for a minimum level of monthly usage. GTE Sprint and Telesaver have minimum monthly charges of $5.

Western Union's long-distance service and AT&T's "Reach Out America" plan charge a minimum of $10, while SBS Skyline charges $15 a month. TDX's minimum monthly rate is $50 for businesses.

A third step in exploring long-distance services is to pay close attention to the "travel plans" and "special discounts" offered by the companies, especially if you make long-distance calls when you are away from home or if you might qualify for a special discount.

Some companies route all long-distance calls made away from home through one central location. So if the company you choose routes its calls through Washington, D.C., and you call from Chicago to Los Angeles, you will be charged as if you called Los Angeles from Washington, which would be more expensive than a Chicago to Los Angeles call.

Complicating the selection process further is the fact that you are not limited to using only the company you have selected as your primary carrier. Consumers who use more than one long-distance phone service might be able to put together the best deal by tailoring the services to their personal calling patterns.

Several plans offer "volume discounts," with the discounts growing as the volume increases. If you make a $20 to $75 long-distance phone call during the day with the GTE Sprint service, you will get a 3 percent discount.

The discount may be different depending on the time of day. While Sprint gives a 9 percent discount for a $20 to $75 phone call made from 5:00 to 11:00 p.m., the same price phone call will receive a 10 percent discount if made after 11:00 p.m. or during the weekend.

Some companies, such as U.S. Telecom with its All-American 6 rate, apply volume discounts to the whole bill. U.S. Telecom gives a 5 percent discount on the All-American 6 rate if a bill exceeds $1,000 per month, and a 10 percent discount if the bill exceeds $10,000 a month.

Other companies give discounts only on a portion of the bill that exceeds a specified amount.

For example, ITT Longer Distance service does not give a discount on the first $15 of the bill. For the next $60, there's a 2 percent discount, and for the next $125, customers get a 5 percent discount.

One often overlooked aspect of cost comparisons is the billing procedures of each company, according to PIRG.

Some companies bill in 60-second increments, which means if you talk for 64 seconds you are billed for two minutes. This difference can be important if a consumer makes a lot of short calls, where an extra few seconds per call can add up to a lot of money.

Another feature to examine is the directory assistance rate for long-distance calls. While Allnet charges nothing for directory assistance calls, AT&T gives you the first two calls free and then charges 50 cents for each additional call.

Quality of service is one factor consumers can't judge from the brochures and often something they can't test before choosing.

"Low rates don't do you much good if you can't get through or if the connection is so bad you can't carry on a conversation," notes Consumers' Checkbook, which tested eight companies and surveyed customers of those eight plus three more.

SBS Skyline's quality of service was rated equal to AT&T's, according to the Consumers' Checkbook study. GTE Sprint and Allnet also rated relatively high, while Western Union and ITT were the companies with the worst quality record -- or the highest percent of calls rated "moderately or severely defective" by test callers or called parties. Some of those quality differences are expected to disappear with equal access.

Many of the long-distance companies, such as AT&T, Sprint and MCI, charge more for the first minute of each call than for subsequent minutes. For callers who tend to make long calls, this is an important feature.

For those who call abroad, it is important to note that while some companies handle international calls to a few locations, so far only AT&T can place calls worldwide. For example, GTE/Sprint can transmit international calls only to the United Kingdom, the Virgin Islands, Australia and parts of Canada. Both AT&T and GTE/Sprint have launched ad campaigns to promote their international service.

Most of the telephone companies set their long-distance rates with reference to distance. But others consider it only indirectly or not at all, which may be more attractive to some callers.

A major feature of many of the alternative services compared with AT&T is that an individual can place calls from many locations other than his regular phone without having to pay an extra operator-assistance or credit-card charge. The travel feature can be as convenient in your home city, if you want to make a call from a pay phone or a friend's house, as it is when you are traveling.