Four members of the polygamist Singer-Swapp family, convicted in a church bombing and standoff that left a Utah lawman dead, have been sent to a federal detention center in California for presentence evaluations.

Meanwhile, Utah federal district judges will convene a rare en banc hearing Friday to consider the constitutionality of controversial new federal sentencing guidelines challenged by two of the defendants.Unnamed sources said that clan matriarch Vickie Singer, her son John Timothy Singer, her son-in-law and ringleader Addam Swapp and his brother, Jonathan Swapp, were flown to San Diego late last week for background reports and psychological evalutions.

The four were found guilty in May of 20 of 23 federal counts stemming from the January bombing of an LDS chapel and the subsequent 13-day stand-off at their Marion, Summit County, farm. Killed in the shootout that ended the siege was Lt. Fred House, a state Corrections officer.

Sentencing was set for July 1, but the evaluations and court hearing make it unlikely the date will be kept or that Vickie Singer's request to be released to a halfway house so she can see her other children will be granted.

Presentence evaluations usually require 30 days and are rarely done in Utah, where there are no federal detention centers. The four still will be able to communicate with their family by telephone.

A challenge to the guidelines was filed last month by Fred Metos, attorney for John Timothy Singer, and then joined by lawyers for Vickie Singer.

The guidelines, effective for crimes committed after Nov. 1, mandate sentence ranges drawn from standardized formulas. Points are added or subtracted for the type of crime, defendant's criminal history, property damage, defendant's remorse and other factors.

Judges may sentence outside the guidelines, but must make specific legal findings, which can be challenged on appeal.

The judges agreed the challenge raised in the case was important enough for a hearing before the full bench, said Jenkins, who presided over the trial.

"In this particular instance the consequence of the motion would have courtwide significance," he said. "Quite frankly, the judges agreed some weeks ago that if the question of constitutionality involving sentence guidelines was raised in any case before any judge, we would consider it en banc."