UPDATE 2-Go Ahead unit Southeastern to cut 300 jobs

* Go-Ahead's rail unit Southeastern to cut 300 jobs in 2009

* Cuts due to lower passenger growth, tougher economy

* UK rail union RMT says cuts are unjustifiable

(Adds background, comment from RMT rail union)

By Philip Waller

LONDON, Jan 9 (Reuters) - British transport operator Go-Ahead Group's (GOG.L) Southeastern rail franchise said on Friday it was planning to cut 300 jobs in 2009 due to lower passenger growth and the economic downturn.

Southeastern, which runs commuter trains from London to Kent, said 90 redundancies would take place in the first quarter, with the rest coming later in the year. It was hoping to achieve much of the latter through natural staff turnover and not filling vacancies when staff retire or leave, it said.

The cuts will affect management, administrative and support roles.

"In line with many other companies in the UK at the moment, this step is being taken in order for us to remain a successful organisation," Southeastern said in a statement.

"It's necessary to take these measures in a time of reduced passenger journey growth and a more challenging economic climate."

Southeastern is a wholly owned subsidiary of Govia Ltd, which is part of Go-Ahead and privately owned French transport operator Keolis. Newcastle-based Go-Ahead also runs the Southern and London Midland rail franchises and buses across the UK.

In September, Go-Ahead unveiled a 19 percent rise in pretax profits in the year to June 28, before amortisation and one-off items, to 131.1 million pounds.

Its rail division increased operating profit by 16.8 percent to 77.2 million pounds, and the company said growth in bus and rail passenger numbers had accelerated.

Britain's Rail, Maritime & Transport (RMT) trade union described the cuts as unjustifiable and said its members would resist them.

"Southeastern is part of a group that has been raking in record profits, and these planned cuts are not only completely unjustified, but underline that Govia is interested only in making money," RMT general secretary Bob Crow said. (Reporting by Philip Waller; editing by Simon Jessop/Will Waterman)