Kaiser Foundation Health Plan switchboards in Northern California have been deluged with calls from worried people ever since the organization announced it would urge 30,000 members to take AIDS tests. Kaiser spokeswoman Susan Pieper said the calls range from people seeking only information to those anxious to have the test as soon as possible. Kaiser, the nation's largest prepaid health-care organization, said last week that patients should take an AIDS test if they received blood transfusions between 1977 and March, 1985, at its hospitals in San Francisco, San Rafael and Vallejo. During that period, the Kaiser hospitals used blood supplied by Irwin Memorial Blood Bank of San Francisco. Irwin officials recently disclosed that as many as one in every 100 units of blood issued from 1981 to 1983 was infected with the acquired immune deficiency syndrome virus. Irwin officials said that since AIDS screening methods were instituted in 1985, their facility is considered one of the safest sources of blood in the United States.