* All major agencies now rate Indonesia investment grade
* S&P has acted years after Fitch and Moody's did
* Jakarta stocks spike on the upgrade news
* C.bank, government welcome the long-sought upgrade (Adds comments from finance minister in paragraphs 20 to 21)
JAKARTA, May 19 (Reuters) - Rating agency Standard & Poor's (S&P) upgraded Indonesia's sovereign ratings to investment grade on Friday, a long-awaited move that sent Jakarta shares soaring on hopes it could spur a wave of investment into Southeast Asia's biggest economy.
Fund managers say the investment grade from S&P, which matches the ratings awarded by Fitch and Moody's years ago, will give Indonesia access to a wider pool of investors. A rating upgrade usually also means an economy can get cheaper borrowing costs when it issues bonds.
S&P upgraded Indonesia's sovereign credit outlook to BBB-, its lowest investment grade, up from the previous junk status of BB+. The agency gave the new rating a stable outlook.
"It's about time," Wellian Wiranto, an economist at OCBC Singapore wrote in a report on the upgrade headlined: "Better late than never."
Fitch upgraded Indonesia to investment grade in December 2011 and Moody's in January 2012.
The main stock index in Jakarta spiked to be up more than 3 percent after the S&P upgrade, the biggest intraday percentage rise since October 2015, and gained 2.6 percent for the day. The rupiah currency also rose and Indonesian dollar bonds rallied.
"Winning the investment grade title allows Indonesia access to a wider investor base. This rating upgrade should drive valuations higher," said Taye Shim, an analyst at Mirae Asset Sekuritas Indonesia.
S&P said the upgrade reflected its assessment of reduced risks to the country's fiscal position.
"Indonesia's increased focus on realistic budgeting has reduced likelihood that shortfall in future revenue would widen general government deficit significantly," it said.
Gundy Cahyadi, an economist at DBS in Singapore, said the upgrade was a "clear indication of Indonesia's improved fundamentals in recent years and investors' acknowledgement of it."
While there may only be a "knee-jerk" positive reaction from markets, Cahyadi said the most significant impact was likely to be on foreign direct investment.
Indonesia is trying to lure investors for a $450 billion infrastructure drive to revive economic growth.
SUCCESSFUL TAX AMNESTY
S&P had previously not followed the upgrade to investment status by other big ratings agencies due to a host of concerns. It gave Indonesia a positive outlook in May 2015 for President Joko Widodo's bold move to remove gasoline subsidies.
In June last year, it denied Indonesia its coveted investment grade again, citing weak government revenue collection and worsening corporate credit quality.
After that, Widodo reshuffled his cabinet and appointed the respected former managing director of the World Bank, Sri Mulyani Indrawati, as his finance minister.
She then ran a tax amnesty program that many said was the world's most successful and is currently overseeing a plan to overhaul the taxation system.
Bharat Joshi, investment director at Aberdeen Asset Management in Jakarta, said the upgrade should cut Indonesia's cost of funds, which is relatively expensive compared with regional peers.
Indonesia dollar bonds jumped by over a point with the bonds due 2027 now indicated at 104.625/105 cents on the dollar. The cost of insuring against default on its sovereign debt also fell. The 5-year CDS was down 6 basis points at 125/130 bps.
Bank Indonesia Governor Agus Martowardojo welcomed the S&P upgrade. BI has said Indonesia deserved an investment grade after a host of improvements in its external balance, including a narrower current account deficit.
Indrawati said the government would now focus on keeping the state budget credible and effective.
"Indonesia will try to reach its development goals without having to resort to an unsustainable budget," Indrawati said, adding that the upgrade could help boost investment and allow Indonesia to reach economic growth of 5.4-6.1 percent in 2018.
In recent quarters, Indonesia has had annual growth of 5 percent or less. (Additional reporting by Hidayat Setiaji in JAKARTA and Umesh Desai in HONG KONG; Writing by Ed Davies; Editing by Richard Borsuk and Nick Macfie)