WASHINGTON (AFP) - The next US president will face tough choices over how to handle terrorist suspects even if the Guantanamo detention camp is closed, as both White House hopefuls have promised, experts say. Democrat Barack Obama and Republican rival John McCain have vowed on the presidential campaign trail to shut down the prison at the US naval base in Guantanamo Bay, Cuba, condemned by allies and rights groups as a legal blackhole. But even if the roughly 270 inmates were moved to a high-security prison on the US mainland, the next commander-in-chief will be confronted with a legal morass left over from President George W Bush's attempts to treat terror suspects separately from the US legal system. "Quite honestly the next president, whoever he is, is going to face a series of difficult decisions. The options are all unattractive," said Sarah Mendelson of the Washington-based Centre for Strategic and International Studies. "The main issue the next president is faced with is a broader issue beyond Guantanamo, which is who should be detained and why?" To avoid the legal and diplomatic fallout created by Guantanamo, the next president will probably have to narrow the definition of who should be detained and focus on key figures in terror networks, Mendelson said. The next president will also have to weigh the future of US-run prisons in Afghanistan and Iraq, as well as CIA detentions and interrogations carried out at secret sites abroad. As for the detainees held at Guantanamo, the next administration would have to decide who could be put on trial - despite evidence tainted by possible torture or abuse - and whether the accused should be tried in US courts or within the special "war on terror" tribunals created by Bush. Senator McCain supports the special tribunals, while Obama's advisers say he would get rid of the controversial tribunals and try the detainees in regular federal courts or in military courts. The president could allow such inmates to be freed, upholding American legal principles but running the risk the suspects later take up arms against US targets. The alternative would be a return to holding detainees indefinitely without charge, a practice employed at Guantanamo that would require a new law and which could once again draw international condemnation. Neither McCain nor Obama has taken a position on introducing open-ended detention - known as preventive or administrative detention - but human rights groups and legal experts are already debating the idea. An adviser to Obama told AFP the Illinois senator would first make full use of the court system before backing any such measure. "My sense is that his inclination will be to exhaust the existing options in our legal system which he thinks has dealt with terrorism cases quite well in the past before creating something new, untested and potentially damaging to our reputation," said the adviser, who asked not be named. McCain's campaign was unavailable for comment. Right-leaning experts are pushing for preventive detention, arguing that modern-day militants who wear no uniforms and act independently of any state fall outside traditional legal definitions and need to be locked up before they do harm. But rights advocates say it would be a slippery slope that backfired on Britain in its fight against the Irish Republican Army and could serve as a recruiting tool for militants. "Such a 'solution' would be worse than the Guantanamo problem," Kenneth Roth, executive director of Human Rights Watch, wrote in the June issue of Foreign Affairs. "Indeed, it would effectively move Guantanamo onshore and make its detention regime a regular part of the US government's arsenal," Roth said.