The Equitable Trust Bank said today it has begun the first nationwide check guarantee service in the Washington-Baltimore area, designed to end the embarrassment and harassment involved in trying to write checks away from home.

The service, intended to boost the use of checks, is also an attempt to return to an era when merchants didn't fingerprint, photograph and scrutinize customers writing checks.

"The consumer is not using his checking account enough," said Rick Warfield, a vice president for the Los Angeles-based Telecredit, In.c, which will operate the program and guarantee the checks. "We're making the assumption that checks are here to stay for a long, long time."

The program allows selected bank customers free of charge and others who pay a $6 annual fee to cash checks at 80,000 participating stores across the country. This is done by presenting a special Welcome Check card with the check, Equitable officials said today.

Telecheck, Inc., however, an unrelated franchising network of check guarantee service companies across the country, said through a spokesman yesterday that it has offered nation-wide check guarantee service for Washington-area customers since 1976.

Equitable Trust has 29 branches in Montgomery and Prince Georges based University National Bank which merged with Equitable in February.

Telecredit expects to have about 3,000 stores accepting the service in the Washington area by the end of the year, an increase from the 500 current member stores, Warfield said.

The two biggest obstacles to check writing today, Warfield said, are the embarrassment-"You're almost treated like a criminal"-and the time-consuming process at most stores. "It's per pressure. You look behind you and there's a line of people with cash waiting for you," Warfield said.

Now many stores require two identification cards or the signing of the check by a supervisor, often in another department or on another floor, Equitable officals said.

In the Washington area many stores use the Telecheck check guarantee system, which is unrelated to Telecredit. Telecheck approves the check written at a store and then pays the mervhant if the check bounces. Telecheck Washington has been under investigation by the Maryland Attorney Generalhs office in connection with complaints of harassing customers whose checks bounced.

"A significant portion of our customers continue to want to use paper checks," said Bruce McPherson, an Equitable senior vice president. However, because of the fear of bad checks many stores will not accept them, he said.

The Telecredit system is not new, Warfield said. The Chase Manhattan Bank in New York and the Central Trust Company of Cincinnati together have about 9000,000 customers using the special Welcome Check cards.

As part of a package with the Cincinnati Bank Telecredit signed up 3,000 stores in Florida to make it easier for the Cincinnati Reds baseball team players and fans to use checks while at the team training camp in Tampa, Fla., Warfield said.

Welcome Check card customers can also cash checks up to $200 to $1,000 at banks across the country, Warfield said.