Nearly one-third of the people who call the government's toll-free telephone number to obtain information about cancer get a busy signal or simply hang up because they have to wait so long, federal investigators say.

The investigators said that the telephone service, run by the National Cancer Institute at a cost of $21.4 million this year, was "the most comprehensive and credible source for cancer information" in the United States. But, they said, it has been operating far below the standards of customer service set by private industry and promised by President Clinton, with his pledge to reinvent government.The toll-free number is 800-4-Cancer (800-422-6237). It receives 600,000 calls a year from cancer patients, their friends and relatives, as well as from doctors and other health professionals.

In a report to be issued next week, June Gibbs Brown, inspector general of the Department of Health and Human Services, said: "In 1997, almost one out of every three attempted calls to the Cancer Information Service failed to reach an information specialist. Busy signal rates for the individual contractors ranged from 10 percent to 52 percent. Networkwide, average busy signal rates for 1995 and 1996 were similar."

The government operates the service through contracts with 19 organizations including the Memorial Sloan-Kettering Cancer Center in New York, the Duke Comprehensive Cancer Center in Durham, N.C., the University of Texas and the Jonsson Comprehensive Cancer Center in Los Angeles.

Florida had the highest busy rate, with half the callers getting busy signals last year.