William H. Wolowitz, 69, a Washington merchant who held patents for typewriter and credit card devices, died Monday at Providence Hospital after an apparent heart attack.

Mr. Wolowitz operated the United Typewriter Co. at 14th and H streets NW, which had been started by his father, from the 1930s until he sold it in 1962.

In 1940, he sold five typwriters for 99c each to stimulate sales on Washington's Birthday.He used to say that this helped start the now-traditional bargain sales in this area on that holiday.

Mr. Wolowitz held patents in the field of plastic credit cards, having thought of using plastic cards with raised letters and a machine that could transfer these letters to credit forms, along with the price of the goods purchased.

In the 1960s, he filed suit in federal court for alleged infringement of these patents. Eventually, the Golf Oil Corp., Humble Oil Co., and Addressograph-Multigraph Corp. and other companies settled "for a seven-figure amount," according to what Mr. Wolowitz said later. His son-in-law, Tevy Schlafman, said the actual amount was about $1.4 million.

Mr. Wolowitz founded the Spellright Corp. of Washington in the 1960s and was granted patents on devices for correcting errors in typing.

One was a ribbon that was half-black and half-white. It enabled the typist to "type-over" a mistake in white and then type the correct character in black. Another was a cartridge, or cassette, that was similar to his ribbon.

In 1976, he settled a patent infringement suit in connection iwth these devices with International Business Machines for $350,000. A provision of that settlement was that IBM was to be allowed to manufacture "self-correcting" business machines without being sued again by Mr. Wolowitz.

Mr. Wolowitz was born in Newark, N.J. He lived in the Washington area for more than 60 years. He earned a bachelor's degree at American University.

He was a Mason and a member of the Shepherd Park Lions Club. He also belonged to Temple Sinai in Washington.

he is survived by his wife, Frances H., of the home in Bethesda; two daughters, Linda W. Schlafman, of Bethesda, and Deborah W. Crown, of Shaker Heights, Ohio; a son, David, of Durham, N.H.; sister, Estelle Jacobs, of Bethesda, and another sister, Rose Moore, and a brother, Ben Wallace, both of Florida.