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Patrick Drahi, founder and head of Altice, a European telecommunications giant.Credit Ed Alcock/M.Y.O.P.

Cablevision has agreed to sell itself to Altice, an acquisitive European telecommunications giant, for about $17.7 billion, including debt, people briefed on the matter said on Wednesday. It is the latest deal to reshape the broadband and cable television landscape.

An announcement could be made on Thursday, these people said.

The transaction would further realign an industry already in upheaval as cable and telecom companies seek greater scale and negotiating power with content providers.

But the takeover of Cablevision — one of the last trophies of the American cable industry and the longtime province of its founding family, the Dolans — could also draw significant concern from regulators, particularly as control of the telecom market shrinks to fewer and fewer players.

Charter Communications, a cable operator with ties to the billionaire John C. Malone, has already agreed to buy Time Warner Cable after its archrival Comcast failed to complete a deal. AT&T recently completed a $48.5 billion takeover of the satellite television operator DirecTV.

And Altice, run by the French-Israeli billionaire Patrick Drahi, has already announced its intentions to build a footprint in the United States, striking a $9.1 billion deal for Suddenlink Communications this spring. The European telecom had also briefly considered a run for Time Warner Cable itself.

Altice and Mr. Drahi have signaled that they are interested in continuing to build a presence in the United States, having conquered huge sections of Europe and the Caribbean. Moving across the Atlantic meant forcing its way into the huge American market, one unencumbered by the Continent’s fragmented national borders and regulators.

Adding Cablevision and its 3.1 million customers would let the European telecom vault into the top echelon of cable companies in the United States, behind only the likes of Comcast and Charter. Its latest acquisition is the main operator in the New York tristate area, and its assets also include the newspapers Newsday and amNewYork.

The Cablevision deal may signal Altice’s appetite for further acquisitions in the American market, with smaller properties like Cox — controlled by its founding family — remaining independent.

For now, Altice does not intend to draw many cost savings by combining Cablevision and Suddenlink, the people briefed on the matter said. But that may change in the future as the company digests its acquisitions.

Under the terms of the agreement, Altice will pay $34.90 a share in cash, 22 percent higher than Cablevision’s closing stock price on Wednesday. That represents an equity value of $9.6 billion. To help finance the takeover, Altice will sell additional shares in itself and draw on financing from three major banks. The two investors that retain a minority stake in Suddenlink, BC Partners and the Canada Pension Plan Investment Board, may buy 30 percent of Cablevision’s equity as part of the transaction.

Talks between Altice and Cablevision began in June, weeks after the Suddenlink deal was struck and after bankers had deluged the European company with pitches for additional deals to pursue, according to the people who were briefed.

At one point during the negotiations with Cablevision, the Dolans had advocated keeping the company’s media properties, including Newsday and the News 12 Networks local news station. But Altice insisted on including them in any deal.

Analysts have long questioned whether the Dolans would be willing to sell Cablevision in a frenzy over cable assets.

Now they have chosen to sell their prized asset to Mr. Drahi, an aggressive deal maker who has drawn comparisons to his former boss, Mr. Malone. Born in Morocco, he has long pursued business, gauging his success by his wealth.

He played in the European telecom markets, founding a company that he later sold to an arm of Mr. Malone’s telecom empire, before founding Altice in 2002, intent on building his own international cable kingdom.

Along the way, Mr. Drahi developed a reputation as a ruthlessly efficient operator who runs a lean business.

The transaction with Altice would not affect other companies controlled by the Dolan clan, including the Madison Square Garden Company, which owns its namesake sports arena and the New York Knicks and Rangers, and AMC Networks, the cable channel company.