WASHINGTON — The Kennedy Center’s Sondheim Celebration, an ambitious mounting of six musicals by Stephen Sondheim, is off to a rousing start, with favorable notices for its first two productions and healthy bookings for every performance.

The four-month festival officially debuted May 12 with “Sweeney Todd,” which drew kudos from critics. The New York Times’ Ben Brantley called Christopher Ashley’s production “handsomely sung” and “richly mounted” and heaped praise on stars Brian Stokes Mitchell and particularly Christine Baranski. Other Gotham crix who headed south for the opening, including John Simon in New York and Linda Winer in Newsday, were equally laudatory.

A week later, Sean Mathias’ “Company” opened to some equally fine notices. Michael Kuchwara of AP said the production “provides further proof that this celebration is essential viewing for anyone who cares about the American musical theater.” In the Washington Post, Nelson Pressley said Mathias’ “beatifully balanced” staging “throbs with sensual energy.”

From a B.O. standpoint, the entire festival was a success even before opening night. “Sweeney” and “Company” are sold out (runs average just 16 perfs), and the others — “Sunday in the Park With George” (opening June 2), “Passion,” “A Little Night Music” and “Merrily We Roll Along” (opening in July and early August) — are headed that way, according to the Kennedy Center.

The center broke its single-day ticket sales record in February when it sold $632,000 worth of ducats at a $76 top. The entire festival is just shy of 80% sold out, per the center.