Speaker J. Dennis Hastert made history this year when he became the longest-serving Republican in that post. Now he is about to go into the books again as one of the few House speakers, and the first in almost 50 years, to rejoin the rank and file.

Defying expectations that he would immediately retire if the Republicans lost their majority, Mr. Hastert is preparing to remain in the House for at least the early months of the 110th Congress while he helps orchestrate a line of succession at home in Illinois and seeks to shape a political ending beyond his party’s defeat....

It has not been the modern model for speakers to step down and go to the back bench. In recent years, they have fallen victim to ethics charges, infighting and defeats in their own districts. Thomas P. O’Neill Jr. retired. Sam Rayburn died in office.

Throughout the history of the institution, most speakers left under one of those two circumstances.

According to Fred W. Beuttler, the deputy House historian, Mr. Hastert will be the first speaker since Joseph W. Martin Jr. of Massachusetts, a Republican, to step out of the leadership completely but remain in the House after holding the top spot. Mr. Martin was speaker from 1953 to 1954. Mr. Rayburn became speaker when the Democrats won in 1955.

Mr. Martin remained the Republican leader until major party losses in 1958 and was a member for a couple of terms until he lost a primary.

“It is pretty unusual,” Mr. Beuttler said of Mr. Hastert’s plans.