RIVERSIDE, Calif. (AP) _ A 21-year-old newlywed who last month first used a brand of tampon that the company has urged women to discard, died of what a coroner said apparently was toxic shock syndrome.

Tammy Bader McNabb of Riverside died Monday at Riverside General Hospital, three days after being admitted with symptoms of the tampon-related disease, said Riverside County Chief Deputy Coroner Carl B. Smith Jr.

''There is no doubt in my mind that it is a toxic shock syndrome death,'' Smith said Friday. ''She had extreme swelling of the body, renal failure and a mass of infection spread throughout the body. We have tentatively classified it as toxic shock syndrome.''

An official cause of death won't be released until autopsy results are available, Smith said laboratory tests on the victim's blood and on the tampon she was wearing showed the presence of staphlococcus aureus, the bacteria that produces the toxin responsible for toxic shock syndrome.

Mrs. McNabb, who moved to Riverside from Reno, Nev., six months ago after getting married, was wearing a Playtex Super Deodorant tampon when she was admitted to the hospital, Deputy Coroner Jim Camp said.

In national advertisements this week, International Playtex Inc. urged women to discard that type of tampon, offering to replace Super, Super Plus or Slender varieties of the menstrual tampons.

The company cited ''some questions about whether or not certain super absorbent substances, such as polyacrylate, increase the risk of toxic shock syndrome.''

Playtex officials were unavailable for comment Friday because of the Good Friday holiday.

The coroner's report said Mrs. McNabb used the tampons for the first time March 26 and complained of body aches, a headache, sore throat and a low-grade fever. On March 28, she started vomiting and had some diarrhea.

Camp said Mrs. McNabb awoke about 3 a.m. on March 29, staggered around and told her husband she couldn't see and was cold.Her fingers, toes and nose were blue by the time the couple reached the hospital.

On March 21, Playtex lost an $11 million suit filed by the family of Betty O'Gilvie of Wichita, Kan., who died of toxic shock syndrome in 1983 after using the same type of tampon worn by Mrs. McNabb.

More than 2,000 cases of toxic shock syndrome have been recorded nationally since the disease was diagnosed in 1980, according to the national Centers for Disease Control, which said Mrs. McNabb's is the first reported toxic shock death this year.