(Adds South Korea, U.S. reaction)

By Jon Herskovitz

SEOUL, April 1 (Reuters) - North Korea made its first mention of South Korea's new president on Tuesday since his December election, using a torrent of insults and warning his call to get tough with Pyongyang would have "catastrophic" consequences.

In the past week the North has test-fired missiles, expelled South Korean officials from a joint factory park in the North and threatened to reduce South Korea to ashes in a show of anger at Lee and the South's ally, the United States.

North Korea called conservative Lee Myung-bak, who took office in February, a "political charlatan", an "absent-minded traitor" and a "U.S. sycophant" in a commentary in the communist party Rodong Sinmun newspaper carried by its KCNA news agency.

South Korea's Yonhap news agency quoted a Lee aide as saying: "North Korea's mentioning of the name of South Korean head of state is not an appropriate attitude."

Lee's government has told its impoverished neighbour that if it wants more aid, it must improve human rights, abide by an international nuclear deal and start returning the more than 1,000 Southerners kidnapped or held since the 1950-53 Korean War.

The stand has infuriated the testy North, used to billions of dollars of aid over the past 10 years from Lee's left-of-centre predecessors whose "sunshine policy" sought little in return.

"The Lee Myung-bak regime will be held totally responsible for ushering in a catastrophic incident by freezing North-South relations and destroying peace and stability on the Korean peninsula through its pro-U.S., anti-North Korea confrontational attempts," the commentary said.

Unusually, the entire commentary was read on a special state television broadcast. This was the first official mention of Lee's victory by the state-controlled media.

"The new thing about this is that he is being vilified by name. (But) it is a much more superficial change than people might think. The bulk of domestic propaganda has always been anti-South Korean," said Brian Myers, an expert on the North's propaganda at the South Korea's Dongseo University.

DEFLECT BLAME

With its taunts, analysts said the North also might be trying to deflect blame from itself for a delay in implementing a deal with regional powers to scrap a nuclear arms programme in exchange for aid and an end to its international ostracism.

The North failed to meet an end-of-2007 deadline in a six-country deal to release a complete accounting of its nuclear material and weaponry, as well as answer U.S. suspicions of having a secret programme to enrich uranium for weapons.

The international community hopes the deal will eventually lead to a complete nuclear disarming of the North.

"The North has shifted to blaming the South for what it has not been able to work out with the U.S.," said Choi Jin-wook, of the Korea Institute for National Unification.

Lee's government has said it would work closely with the United States and Japan, and its stance on North Korea puts South Korea closer to its traditional allies in trying to exert pressure on the North to force change.

Christopher Hill, the chief U.S. envoy to the North Korean nuclear talks, said in Seoul that the comments "are obviously completely inappropriate" and called on the North to make progress on the nuclear deal.

Lee has proposed an aid package for North Korea that would lift per-capita income from a few hundred dollars a year to $3,000, provided it abides by the six-way nuclear deal.

The North called Lee's plan "piffle" and said it "will be able to live as well as it wishes without any help from the South as it did in the past". (Additional reporting by Yoo Choonsik and Lee Jiyeon; Editing by Jonathan Thatcher)

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