BOSTON — The state pension fund hemorrhaged $4.1 billion through August and then lost nearly $4 billion in September alone, battered by collapsing financial markets.

The losses, which have driven the fund balance down to $45.7 billion from $53.7 billion back in January, could take years to recover from, according to fund officials. The drop in value has the fund on course to post its largest annual losses in its 25-year history. The numbers don’t reflect losses incurred in early October.

State Treasurer Tim Cahill, who is separately enmeshed in efforts to get the state back into the frozen short-term borrowing market, urged board members to stay calm during a pension board meeting on State Street yesterday.

“If you stay invested for the long term, these markets will come back,” said Cahill, who chairs the board that oversees fund investments. “Now is not the time to panic.”

Cahill said state retirees, whose pensions depend on the fund’s assets, would not feel any pinch from the fund’s recent losses. “We’ll meet all of our obligations,” he said.

The Pension Reserves Investment Trust is down 15.3 percent this year. It took the fund a year to recover from the 1987 stock market collapse and nearly four years to regain asset values that disappeared after the dot-com bubble burst at the start of this decade.

“As investors, we can only get what the market is willing to give us,” said Michael Travaglini, executive director of the fund. “This will likely be the PRIT fund’s worst year in its history from an absolute return perspective. Anyone who’s in a 401(k), anyone who’s an investor of any type is sharing the same experience.”

The PRIT fund was created by the legislature in 1983 to reduce the state’s unfunded pension liability. Cahill chairs a fund board that works with investment firms to boost the fund and pay public pensioners.

Travaglini said the fund’s annual 8.25-percent return target would likely not be hit this year, but said the fund was still exceeding its long-term goal, averaging just shy of 11 percent annual returns since 1985.

While the fund balance now rests at the same level as at the end of 2006, pension fund managers say the fund, despite the heavy losses, outperformed the market, which was down 19 percent through September.

“In the context of everything that’s going on, it’s actually not that disappointing,” the treasurer said after the meeting. “It could be far worse.”

During staff updates on the fund’s performance, chief investment officer Stan Mavromates said the economy tends to lag stock market trends by about six months, so the full effects of the recent market slides would not be felt until spring. He warned board members to stay focused on long-term goals.

Travaglini said the fund took its worst hits in U.S. and international stocks, which comprise about 45 percent of the fund’s entire portfolio. The fund’s domestic equity investments are off 12 percent year-to-date through August, with international investments down 15 percent and investments in emerging markets losing 22 percent.