NEW YORK, April 9 (Reuters) - Ratings of real estate investment trusts will likely slip closer to junk territory as commercial real estate remains in a slump, Standard & Poor's said on Thursday. "We do view the sector as investment-grade-worthy but it is under stress and we expect it to continue to be under stress," S&P analyst Lisa Sarajian said on a conference call. The sector will likely migrate to the low end of the investment-grade category, she added. S&P earlier this week downgraded its ratings on six real estate companies and assigned or affirmed negative outlooks on another seven, indicating a downgrade is likelier over the next two years. Within the past month, S&P has cut three real estate companies to junk status and more downgrades are likely, Sarajian said. "The new normal looks a little more like our downside," she said. Though few real estate companies are in the same straights as General Growth Properties Inc, a large mall owner that has warned it could file for bankruptcy protection, troubles may surface at more companies as the weak economy weighs on building occupancies and rental rates, S&P said in a report released on Thursday. Some of real estate companies' troubles are being masked because in-place leases are helping cash flow for now, S&P said. "While it's possible that the economy could recover before cash flows deteriorate substantially, our base-case scenario analyses generally assume a 5 to 15 percent drop in net operating income through 2010," the report said.