MCI Communications Corp., in a battle to sign up as many customers for long-distance service as possible, has enlisted the help of Amway Corp., the largest direct-sales company in the United States, to market MCI along with a battalion of products from soap to satellite receivers.

MCI, which began testing the idea last spring, yesterday said it had signed up "several hundred thousand accounts" through Amway representatives. "Amway is selling our services all over the country," said MCI spokesman Gary Tobin. "Amway can make calls on people individually, they can pass out fliers, set up booths, collect 'equal access' ballots for us, or they can telemarket, get an affidavit signed in writing and turn the customer over to us."

The "equal access" or dial-one process, mandated by the breakup of the Bell System breakup, gives customers a choice of direct-dial long-distance service by eliminating the lengthy codes customers previously had to dial to reach competitors of American Telephone & Telegraph Co. One-third of all telephone lines in the country now have the service, and the process is expected to be complete by September 1986. MCI is targeting both direct-dial long-distance customers and those that must still use a code to reach MCI's service.

Analysts and consumer advocates said yesterday that the arrangement could ty if there are questions.

The pluses of the Amway arrangement include giving MCI a built-in sales force of 750,000 in 50 states. Using that force will allow MCI to market where it ordinarily would not and it can also cut costs, said Tobin.

"There is some cost involved in advertising, direct mail and telemarketing," which is the standard approach, he said. "Amway has a cost in it too, but it's advantageous to us."

Amway's Bennett said Amway, which has more than $1 billion in revenue annually, is looking to expand and retain its sales force by offering salesmen a cut of a customer's monthly MCI long-distance bill. Salesmen receive a bonus of between $8 and $20 for signing up a residential or commercial customer, plus 1.2 percent of the overall monthly long-distance bill, he said.

Bennett said Amway does not get a cut of the salesman's bonus. "One of the benefits is the distributor is more likely to stay in the business, so it's an incentive for us," he said.

MCI officials would not discuss their financial arrangement with Amway.