PITTSBURGH (AP) _ Mayor Richard S. Caliguiri said today he is suffering from a rare, life- threatening disease, but said he is not impaired and will not resign.

Caliguiri, 55, said he is suffering from amyloidosis, a disease that attacks vital tissues and organs. He said the disease was diagnosed 6 1/2 months ago, when he fell ill while playing golf.

Caliguiri's doctors said the disease is so rare and poorly understood that there is no reliable way of forecasting its consequences, The Pittsburgh Press said today.

Caliguiri, a Democrat who has been in office for 10 1/2 years, earlier had announced his intention to seek re-election in 1989.

''I have been and remain today fully capable of discharging my responsiblity as mayor,'' he said in a statement. ''At the same time, I have an obligation to myself and to my family to guard my health and, God willing, to beat this thing, which is precisely what I mean to do.''

The mayor said the disease causes the body to produce excess amounts of proteins.

''The result ... can be no more than a nuisance, at one extreme, to a life- threatening situation, at the other,'' he said.

The Pittsburgh Press, which first reported on the mayor's illness, said amyloidosis deposits protein substances in tissues and organs, leading to impairment and possible failure of the heart, kidneys, gastrointestin al system, respiratory system, nervous system, joints, skin and blood.

Caliguiri said his heart and gastrointestinal system have been affected.

''In my particular case, thankfully, the disorder was discovered at its early stages and through medication its advance seems to have been arrested,'' the mayor said.

The mayor entered a hospital a week after suffering a dizzy spell while playing golf March 7.

Since then, he has refused to discuss his health, but has looked gaunt and pale.

''I've kept it to myself for my own private, personal reasons,'' Caligiuri told the Press.