US STOCKS-Wall St flat, paring losses on Greece hopes
* Investors watching situations in Greece, Ukraine
* S&P 500 coming off record closing high
* Celsus shares plummet after drug fails study
* Dow, S&P 500 and Nasdaq all flat on the day (Updates to afternoon trading)
By Ryan Vlastelica
NEW YORK, Feb 17 (Reuters) - U.S. stocks were flat on Tuesday, paring modest early losses and putting the S&P 500 back near record levels as optimism grew that a debt deal would be reached with Greece.
A source told Reuters that Greece intends to ask for an extension of a loan agreement tomorrow. The report follows a collapse of deal negotiations on Monday, which led to European Union finance ministers pressuring the country to remain in an international financial rescue program. U.S.-listed shares of the National Bank of Greece fell 8.7 percent to $1.47.
The news was viewed as another sign of progress, building on the recent optimism that contributed to major indexes notching a second straight week of solid gains last week.
Despite that, investors continued to monitor the situation cautiously, while a fragile Ukraine truce added to the market's uncertainty. Continuación...