WASHINGTON — Matthew G. Whitaker, the acting attorney general, has decided not to recuse himself from the Russia investigation, despite being advised otherwise by a career ethics official, according to a Justice Department letter sent to Senate leaders. Mr. Whitaker will now have final say over any major developments made in that inquiry.

[Read the letter.]

The deputy attorney general, Rod J. Rosenstein, who has been overseeing the investigation while Mr. Whitaker spoke with ethics lawyers, will continue to manage it day to day, according to a senior department official, who was not authorized to speak publicly on the matter.

Mr. Whitaker has not yet been briefed on any aspect of the investigation, although one of his advisers has been briefed on major developments, according to the senior department official. That adviser has not shared information with Mr. Whitaker, and it is not clear when the acting attorney general will have his first briefing.

Mr. Whitaker must now be informed of any “significant” prosecutorial or investigative steps in the Russia inquiry, which is being led by the special counsel, Robert S. Mueller III.