(For a Reuters live blog on U.S., UK and European stock markets, click LIVE/ or type LIVE/ in a news window.) * Weekly jobless claims unexpectedly rise * Micron jumps after upbeat revenue forecast * J&J shares slip on problem with COVID-19 vaccine batch * Indexes up: Dow 0.17%, S&P 0.84%, Nasdaq 1.71% (Adds comment, details; updates prices) April 1 (Reuters) - The S&P 500 on Thursday crossed the 4,000 mark for the first time, as gains in technology shares as well as optimism about a pickup in economic activity helped Wall Street kick off the second quarter on a high note. Swift vaccinations and a massive fiscal stimulus program are powering a recovery in the labor market, helping investors shrug off latest data that showed a rise in the number of Americans filing new claims for jobless benefits last week. The closely-watched monthly jobs report on Friday could show the U.S. economy added 647,000 jobs in March, on top of a 379,000 increase in February. There is also optimism about President Joe Biden’s $2 trillion-plus infrastructure plan that would bring more investment into building roads and bridges and tackling climate change. The 4,000 level “could be a possible inflection point where it renews confidence that this bull cycle is not over and that equities can remain resilient in the face of heightened interest rates and perhaps a not as extremely accommodative Fed policy,” said Matt Hanna, portfolio manager at Summit Global Investments. It took the benchmark index about a year-and-a-half to close the 1,000-point gap to 4,000, compared with about five years from 2,000 to 3,000 points. The blue-chip Dow is less than 1% below its own record high, while the Nasdaq is about 5% off its all-time high as a rapid rise in U.S. bond yields accelerated a rotation from richly-valued tech stocks to underpriced economy-linked stocks. Seven of the 11 S&P sectors rose, with technology and communication services and energy gaining more than 1%. “April is usually a pretty good month for the market historically and I would expect that momentum to continue especially as we see the economy strengthen,” said Larry Adam, chief investment officer at Raymond James. Micron Technology Inc jumped 4.8% after the chipmaker forecast fiscal third-quarter revenue above Wall Street estimates due to higher demand for memory chips, thanks to 5G smartphones and artificial intelligence software. U.S.-listed shares of rival Taiwan Semiconductor rose 3.8% on its plan to invest $100 billion over the next three years to meet the rising chip demand. The technology-heavy Nasdaq jumped 1.7% as “high flying” stocks including Amazon.com Inc, Apple Inc, Alphabet Inc, Microsoft Corp and Facebook Inc added between 1.1% and 2.3% after underperforming last month. At 10:34 a.m. ET, the Dow Jones Industrial Average was up 56.45 points, or 0.17%, at 33,038.00, the S&P 500 was up 33.19 points, or 0.84%, at 4,006.08. The CBOE volatility index slipped below 18 points for the first time in 14 months, a level last seen before the coronavirus-driven global financial market meltdown in March 2020. Johnson & Johnson fell 1% after the drugmaker said it had found a problem with a batch of the drug substance for its COVID-19 vaccine being produced by Emergent Biosolutions . Emergent’s shares tumbled 14.3%. Advancing issues outnumbered decliners by a 2.80-to-1 ratio on the NYSE. Advancing issues outnumbered decliners by a 2.80-to-1 ratio on the Nasdaq. The S&P index recorded 15 new 52-week highs and no new lows, while the Nasdaq recorded 53 new highs and six new lows. (Reporting by Devik Jain and Medha singh in Bengaluru; Editing by Arun Koyyur)