LONDON — British energy giant BP PLC on Tuesday reported a 67 percent drop in third-quarter profit as it took an additional charge of $7.7 billion to cover costs related to the worst oil spill in U.S. history.

Net income at the firm still troubled by its role in the Gulf of Mexico incident last April tumbled 67 percent to $1.79 billion in the quarter.

On a sequential basis, however, the results marked BP’s return to profit after it posted a $17.2 billion loss on charges of $32.2 billion in the second quarter.

The additional $7.7 billion charge stemmed in large part from the later-than-expected capping of the ruptured well, BP said Tuesday. It brought the company’s estimate of the likely cost of the spill to $39.9 billion.

Setting aside the rising bill, BP’s operational results actually improved year on year. Adjusted replacement cost profit, which strips out one-time items and changes in the oil price, rose 18 percent to $5.5 billion, topping the consensus forecast of $4.6 billion.

BP’s net profit decline comes after some of its biggest rivals, including Exxon Mobil Corp., Royal Dutch Shell PLC and Total SA, delivered large profit increases this quarter on the back of a 13 percent rise in oil prices and renewed demand for energy amid the global economic recovery.

The earnings report was the first under the new chief executive, Robert Dudley, who replaced gaffe-prone Tony Hayward on Oct. 1.

“”The results demonstrate that BP is in recovery mode,”” Dudley told reporters at a news conference in London. He added that the company’s “”strong operating performance”” this quarter showed “”the determination of everyone at BP to move forward and rebuild confidence after the terrible events of the past six months.””

Dudley also reaffirmed BP’s intention to start paying a dividend by the end of 2011. The dividend issue will be discussed in February and no decision will be made until then, but Chief Financial Officer Byron Grote noted that the “”improving financial condition of the company and the strength of disposal proceeds are encouraging.””

In order to foot the bill for the accident, BP aims to sell assets of up to $30 billion over the next 18 months. Sales agreements are in place for roughly $14 billion of assets, the company said Tuesday.

Within the same 18-month time frame, BP also plans to reduce its debt level to a range of $10 billion to $15 billion from $23 billion at the end of June. Cash held at the end of the quarter was nearly $13 billion.

Since taking over, Dudley has split the exploration and production division into three and created an independent safety division.

Production declined 4 percent in the third quarter, partly as a result of the spill. It is not expected to grow again until 2012, as BP sells assets.

The firm, despite the incident, remains committed to deepwater drilling in the Gulf, though it won’t be the first to resume operations there and has yet to decide what to do with the rigs sitting idle.

Last Thursday, rival Royal Dutch Shell warned that the impact of the deepwater-drilling moratorium, imposed in the wake of the spill, could be felt for another two years, though the ban was lifted last month.

Part of the reason why oil companies like BP are unsure about when they might be able to start drilling again in the Gulf is that procedures and safety requirements could change again as several investigations draw their conclusions.

The U.S. presidential commission investigating the accident, in its first official finding, last week concluded that contractor Halliburton Co. used flawed cement in the well, which it said could have contributed to the blowout on April 20 that led to the spill.

While not absolving BP of responsibility for the incident, the report strongly criticized Halliburton’s cement job, triggering concern among investors that it may be asked to pay some of the cleanup costs.

BP said Tuesday it would charge interest on the costs.

The commission, appointed by President Barack Obama in May, is scheduled to present its interim findings next week and its final report in mid-January.

In its own investigation report released in September, BP concluded that “”multiple companies, work teams and circumstances contributed to the accident”” and recommended the adoption of stronger minimum requirements, in particular for its drilling partners.