US STOCKS-Nasdaq on track for first closing record since 2000

* Nasdaq breaches closing record last hit in March 2000

* S&P 500 hits intraday record high

* Indexes: Dow up 0.5 pct, S&P up 0.5 pct, Nasdaq up 0.7 pct (Updates to afternoon trading)

By Caroline Valetkevitch

April 23 (Reuters) - The Nasdaq Composite, the U.S. market index most closely associated with technology stocks, jumped to a 15-year high on Thursday and was on track for its first record high close since the tech bubble burst.

The Nasdaq jumped as high as 5,073.091, led by shares of Apple (NasdaqGS: AAPL - news) , which has been among the biggest positive influences on the index in recent years. The index's last record close of 5,048.62 was hit on March 10, 2000.

The S&P 500 was also on track for a record closing high and hit an intraday high in late afternoon trading. Its most recent record close was 2,117.39 on March 2.

Rapid growth in biotechnology companies such as Gilead and social media firms like Facebook (NasdaqGS: FB - news) , driven by the popularity of mobile computing, have also helped to lift the Nasdaq to its current levels.

Shares (Berlin: DI6.BE - news) of Gilead were up 1 percent at $105.23, while Facebook, which late Wednesday posted quarterly revenue that missed analysts estimates, was down 0.8 percent at $83.99.

Shares of Apple, the most valuable company in the United (Shenzhen: 000925.SZ - news) States, were up 0.9 percent at $129.72, while Google was up 1.5 percent at $547.17.

Strategists say there is still room for the Nasdaq to rise.

Stephen Massocca, chief investment officer at Wedbush Equity Management LLC in San Francisco, said the Nasdaq has a good chance of sustaining its current high levels for some time unless there is a significant change in monetary policy.

But he cautioned that social media stocks within the sector will likely tumble eventually. "I think this is the heart of the story and the speculative fervor. I don't know when it's going to end but I know how it's going to end, badly," Massocca said.

At 3:11 p.m. the Dow Jones industrial average rose 82.51 points, or 0.46 percent, to 18,120.78, the S&P 500 gained 10.7 points, or 0.51 percent, to 2,118.66 and the Nasdaq Composite added 32.69 points, or 0.65 percent, to 5,067.86.

Massocca referred to the dramatic rise of the Global X Social Media index ETF, which was up just 0.1 percent on Thursday but is up more than 15 percent for the year so far.

The Nasdaq Composite's market capitalization is at $8.2 trillion, compared with a $19.5 trillion market cap for the S&P 500, according to Thomson Reuters data.

Though the Nasdaq is heavily associated with technology, the S&P 500 technology sector is actually down about 21 percent since March 10, 2000, according to S&P-Dow Jones Indices analyst Howard Silverblatt.

On Thursday, nine of the 10 major S&P sectors were higher, with the energy sector up 1.2 percent following gains in oil prices.

Shares of Dow component Caterpillar (NYSE: CAT - news) gained 1.1 percent to $85.77 following its results.

Advancing issues outnumbered declining ones on the NYSE by 2,170 to 846, for a 2.57-to-1 ratio on the upside; on the Nasdaq, 1,747 issues rose and 980 fell for a 1.78-to-1 ratio favoring advancers. (Additional reporting by Tanya Agrawal, David Randall, Sinead Carew and Rodrigo Campos; Editing by Savio D'Souza and Nick Zieminski)