The State Government is preparing to rush in the trouble-plagued myki ticket system to fulfil a political promise to have it operating in Melbourne in 2009, despite it not being ready to work on trams or buses.

Public Transport Minister Lynne Kosky is set to announce that the $1.35 billion system will be introduced by Thursday - but on trains only.

This means anyone who validates a myki card on a train and then tries to use it on a tram or bus will be potentially liable for a $172 fine for travelling without a valid ticket.

It is expected to take another two to three weeks before the new cards will operate on trams and buses.

The old Metcard ticket system will run alongside myki for at least six months before being shut down.

About 1000 Government workers have been trialling myki cards in the metropolitan area over the past eight weeks, with varying results.

While ticket validators on train stations have worked well during the testing, there have been continuing problems getting the machines to transmit data reliably from trams and buses to the central database.

A transport sector source close to the project said a tiny number of transactions had not been recorded properly by ticket validators on trams. ''If [validators are] not working well enough, someone's transaction might not be … properly accounted for. That's an issue.''

The state agency responsible for myki, the Transport Ticketing Authority, has been debating for three weeks whether to stage the rollout of the system, beginning with trains.

With the trains-only launch, ticket inspectors will be told to ''take a common-sense approach'' to issuing fines on buses or trams to people who have a myki card that may have already been validated on a train.

Ms Kosky, who cancelled leave over Christmas to be in Melbourne to launch the system, is believed to be furious with senior figures at the Transport Ticketing Authority for failing to have myki working across Melbourne.

The authority, along with the Kamco consortium that is building the smartcard system, had promised Ms Kosky the ticket would be ready to run across the city's public transport network by before Christmas.

Both Ms Kosky and Premier John Brumby have repeatedly pledged to have the system running in Melbourne by the end of 2009.

Opposition Leader Ted Baillieu said the introduction of myki had turned into a farce, and attacked Ms Kosky and Mr Brumby for not explaining what was happening.

''Lynne Kosky has disappeared, John Brumby has disappeared, and myki is somewhere out there in the ether and Victorians are none the wiser,'' Mr Baillieu said.

Ms Kosky's spokesman, Stephen Moynihan, said myki would be introduced in Melbourne before the end of the year.

The myki system is based around a re-useable, credit-card sized smartcard that passengers will hold up to electronic validating panels at train stations and on buses and trams.

Passengers will ''touch on'' at the start of each trip by placing the card on the panel, which will issue a green light to indicate proceed, or a red light if the card holder doesn't have enough credit. Passengers must also ''touch off'' at the end of a trip to ensure they get the lowest fare.

The myki system has been running on buses in Geelong since December last year, and in five other regional centres since March. There have been some teething problems, including almost 11,000 instances of overcharging.

The myki project is $350 million over budget and was to have begun operation on March 1, 2007, when the existing contract with Metcard's operator ERG expired.

Design, construction and launch costs will total $850 million, and it will cost another $500 million to operate it over 10 years.

Myki cards will initially be sold online at myki.com.au.

By CLAY LUCAS