CONGRESS is preparing to give President Bill Clinton a tough ride as he tries to push through plans to resume nuclear testing in response to China's blast. Officials are divided over the value of putting testing technology back in place, and senators yesterday joined forces to block any resumption. Twenty-four senators from both parties signed a letter to Mr Clinton, drafted by Democrat Carl Levin, urging him not to resume tests while he was trying to get global accord for a comprehensive test ban by 1996. Mr Clinton announced that in response to the Lop Nor blast, he had asked the US Energy Department to make preparations for possible testing next year. He had also had talks with Britain and France. However, under a tough amendment passed by Congress last year, the White House must seek legislators' approval for new testing. Both houses can also pass a joint resolution forbidding such a test. Two of the influential senators who passed that amendment, Democrat James Exon and Republican Mark Hatfield, have joined Mr Levin's movement to prevent the President from resuming tests. Mr Levin's letter said: ''We believe it would be highly inappropriate and counter-productive for the US to precipitously conduct a test of our own in response [to China's].'' It warns that US tests could incite Russian hardliners to conduct their own tests. It would also undermine the goal of achieving a comprehensive ban by 1996. In addition, America's arsenal was safe and reliable enough not to need further tests, Mr Levin said. America could not encourage other countries to abide by a moratorium while it was pursuing its own tests, he said. Energy Secretary Hazel O'Leary said she backed Mr Clinton's stand. adding that her department would make sure testing facilities were ready at the country's Nevada desert blast site if Congress approved such a move.