A new era at Goldman Sachs is taking shape.

The Wall Street giant’s president, David M. Solomon, is likely to be named chief executive officer by the end of this year, and he is already structuring his senior management team, according to people familiar with the firm’s plans.

The time frame for Mr. Solomon’s ascension has evolved since he was named sole president of the firm in March, establishing him as the heir apparent to longtime Chief Executive Lloyd C. Blankfein, who is 63. But exactly when Mr. Solomon would take over from Mr. Blankfein, who colleagues say remains as engaged as ever in running Goldman, was not then clear. Mr. Blankfein said in an April television interview that his successor needed time to get better acquainted with parts of the company where he had never worked.

Yet in recent weeks, Mr. Blankfein has quietly laid the groundwork to step down late this year. His exit will likely take place in conjunction with the firm’s annual dinner for retired partners in December, two people said. Mr. Solomon, who is 56, would step in shortly after that.

The timetable is not settled and could change, these people cautioned.

Given what is likely to be a relatively short run-up to his promotion, Mr. Solomon is starting to sketch out the possibilities for a new management team, according to Goldman employees.