For the first time since 2000, AMR, parent of American Airlines, posted a first quarter profit today.

The airline reported a net profit of $81 million, or $0.30, in the first quarter, compared with a loss of $92 million, or $0.49, in the same quarter of 2006. Analysts had expected AMR to earn $0.31a share.

However, much of the airline’s improved financial strength came as the result of increasing revenues from International operations — not U.S. domestic routes.

Revenue per available seat mile was up 19% on the airline’s Pacific routes, compared with a 10.3% gain on Latin American routes and a 9.7% increase on Atlantic flights. But domestically, RASM increased only 1% over last year.

Meanwhile CASM increased 0.9% to 10.91 cents/mile. This was 1.6 percentage points higher than forecast. The airline blamed bad weather for the increased costs — saying that the airline was force to cancel 2.9% of its first quarter flights.

American expects CASM to increase 2.1% from a year earlier. Excluding fuel, expenses are estimated to increase 1.1%.

Jamie Baker, analyst with JP Morgan said in a note this morning that the airline’s future guidance is “discouraging.” He said that the airline’s revised cost forecasts “call into question the achievability of its full-year plans.”

Tomorrow? Both Continental and Southwest Airlines report first quarter numbers.