Electoral districts being redrawn

The reshuffling, which became necessary when the state lost a congressional seat as a result of the federal 2010 census, is likely to keep the two Western Massachusetts districts intact, particularly if 20-year incumbent John Olver of Amherst, who turns 75 next week, seeks reelection as he has said he will.

That creates a difficult mapping problem for the Legislature’s Democrat-dominated joint committee on redistricting, which is tasked with redrawing congressional district lines in the coming weeks.

Adding to the crunch is the Eighth District, which contains most of the city of Boston and has a majority nonwhite population. That seat, now held by Michael E. Capuano of Somerville, will probably be held harmless, the sources said.

The fallout that state lawmakers want most to avoid is a federal lawsuit. A decade ago, redistricting resulted in dozens of suits around the country; lawmakers fear a legal battle here this time around.

The redrawing is also made more difficult by what many say is the committee’s decision not to put Niki S. Tsongas of Lowell, the only female in the delegation, in political jeopardy.

On top of that are considerations that the committee will give to those incumbents who have heavy clout in Washington.

Frank is the ranking member of the House Financial Services Committee; Richard E. Neal of Springfield is the likely next chair of the Ways and Means Committee if the Democrats regain control of the House; Edward J. Markey of Malden is dean of the delegation and a senior member of the energy and commerce committee; Olver of Amherst is a senior member of the appropriation committee; and James P. McGovern of Worcester is slated to be the Democrat’s next chairman of the rules committee.