UNITED NATIONS – Syria said yesterday it would not allow a United Nations investigation team to interview President Assad, setting the stage for an escalation in the growing rift between the Damascus Baathist regime and external forces led by America and France.

The renewed request to interview Mr. Assad and his foreign minister, Farouk al-Sharaa, followed a televised interview over the holiday weekend with a man who was once a top regime insider and a former vice president of Syria, Abdul-Halim Khaddam. The interview has led several observers in the region and beyond to wonder out loud about the viability of the current Damascus dictatorship.

Mr. Khaddam was ousted by the Assad inner circle last summer and is now living in exile in Paris. He said in the interview that Syria threatened the former Lebanese prime minister, Rafik Hariri, weeks before Hariri was assassinated in a car bombing in Beirut in February that also killed 20 others. The account of the threats previously was detailed in a report last October by the U.N. team investigating the Hariri assassination.

What Mr. Khaddam said “corroborated information we have from other sources,” a spokeswoman for the U.N. investigation team told The New York Sun yesterday.

Another diplomat familiar with the investigation added that the renewed request to interview Messrs. Assad and al-Sharaa was made by the outgoing director of the U.N. team, the German investigator Detlev Mehlis, and not by his expected replacement, Serge Brammertz.

Mr. Brammertz, a Belgian lawyer specializing in organized crime and international terrorism, has been picked by Secretary-General Annan to replace Mr. Mehlis. An official announcement of the nomination is expected on January 11, Mr. Annan’s spokeswoman, Marie Okabe, said last week.

Mr. Mehlis has in the past asked for interviews with the Syrian president and his foreign minister but only yesterday did the spokeswoman for the investigation team confirm the request.

The Syrian response came swiftly. Several European news agencies reported that various Damascus officials said Mr. Assad will not appear in front of the committee. In the past, Syria refused to cooperate with several requests from the committee, only to compromise later. Mr. Annan has talked almost daily with Mr. Assad in an attempt to mediate a diplomatic compromise.

“For how long will we have to receive the requests of the commission through the media instead of the official channels?” the Italian news agency AKI quoted the president of the Syrian parliament’s foreign affairs committee, Numayr Ghanem, as saying. The Syrian government, he added, had received no request to interview Mr. Assad from the U.N. commission.

But the commission’s spokeswoman said Mr. Mehlis’s team “has already requested the interviews” with Mr. Assad and with Mr. a-Shara, as well as “others” in Damascus. The spokeswoman, who asked the Sun not to identify her by name, said the commission also wants to interview Mr. Khaddam, “as soon as possible.”

In Syria, Mr. Khaddam quickly became the regime’s public enemy no. 1. The official daily Al-Thawra reported plans to try him on “high treason” charges and open an inquiry into “corruption in a series of matters which will include seizing his assets.”

Although no quick Security Council action is scheduled for today, the new developments were expected to increase the international pressure on Damascus. “We strongly support the commission’s investigative efforts,” the American ambassador at the United Nations, John Bolton, said in a statement yesterday. “We expect the government of Syria to comply with these requests fully and unconditionally as the Security Council resolutions require.”

Mr. Khaddam’s damaging testimony made waves in neighboring Israel as well. A Labor Party Knesset member, Danny Yatom, who was formerly head of the Mossad, Israel’s foreign intelligence unit, told Israeli reporters that the words of Mr. Khaddam, an insider who was once considered a top Syrian regime favorite, represent a significant step in the collapse of the Assad regime.

Officially, Israel has not commented on Syria’s travails, indicating ambivalence among policy makers on the prospects of the demise of the Assad regime. Another Labor Knesset member, Ephraim Sneh, told the Sun yesterday that Mr. Haddam’s interview showed a new “loss of cohesiveness” among the Assad family “most intimate” group of advisers. But when asked if he expected their collapse anytime soon, he said,”I would not jump to conclusions.”

Mr. Sneh, a former army general, added that right now any “positive” opposition forces that could replace the ruling Allawite Syrian minority are weak and poorly organized. A collapse of the regime, he said, might lead to Syria being overtaken by a better-financed, Saudi-inspired, “extremist Wahabi” Sunni opposition.

“Bashar Assad may not represent our greatest dreams,” Mr. Sneh said, “but whoever replaces him might be much worse.”