The number of federal prisoners could roughly double to 83,000 in the next five years and may nearly quadruple in 15 years, the U.S. Sentencing Commission said in a report yesterday.

The panel, set up by Congress to write mandatory sentencing guidelines for federal judges, said that natural growth in convictions and recent anticrime laws will account for most of the increase, with the commission's guidelines boosting it further.

Even if the commission's more conservative estimates prove true, growth in the inmate population will worsen a severe overcrowding problem in federal prisons. It will also intensify the conflict between the public's desire for safer streets and its aversion to tax increases.

"The bottom line, worst-case figures are sobering and shocking," said H. Scott Wallace, legislative director of the National Association of Criminal Defense Lawyers. "This is madness."

He said it was "unimaginable" that Congress would fund enough new prison beds "to keep up with this incarceration obsession."

The annual cost of housing federal prisoners averaged $14,520 in 1985, according to the Criminal Justice Institute, a private research group. This ranged from $30,909 in Alaska to $7,023 in Mississippi.

Federal prisons across the country currently hold 43,000 inmates, which is 53 percent more than their intended capacity. The Justice Department's Bureau of Prisons says another 2,636 beds are under construction.

The Sentencing Commission's "high growth" scenario, using a current baseline of 42,000 prisoners, said the population could reach 72,000 to 83,000 in 1992, and between 136,000 and 165,000 in 2002. Under a "low growth" scenario, the panel said, the inmate population would rise to between 68,000 and 76,000 in five years, and 91,000 to 111,000 in 2002.

The high-growth scenario assumes that federal judges will generally follow the commission's sentencing guidelines, which will become law in November unless they are vetoed by both houses of Congress.

The guidelines give judges less discretion in sentencing, although they allow judges to deviate if they explain reasons in writing. The guidelines also would abolish early release through parole in favor of "real-time" sentences.

The high-growth estimates also assume that prosecution and conviction rates will rise and that sentences reached under plea bargains will increase. The more conservative scenario assumes that convictions and sentences will level off, and that judges will give less severe sentences by departing more frequently from the guidelines.

The panel attributed most of the increase to natural growth and mandatory sentences under recent antidrug legislation and a 1984 law aimed at career criminals. It said its guidelines would have a secondary effect.