The State Opposition has promised to deliver 500 extra police officers over four years if it wins the March election.
The initiative would cost $162 million.
Mr McGowan has also promised to spend an extra $1.5 million over two years to expand the mounted police section.
He says the pledge will help to make up for the Government's broken commitment.
"Before the last election, Mr Barnett promised 500 additional police officers; they have delivered 180," he said.
The Premier Colin Barnett has rejected the claims.
He says 150 auxiliary officer positions have been filled and another 170 police will be sworn in over the next 18 months.
"We are exactly delivering what we promised," he said.
"The Government has a program, which is not yet complete, for 500 additional police officers by 2013/14, that project is still going ahead and is on time and we're actually achieving the numbers.
"The promise at the last election is on time, on track and that will deliver 350 sworn officers and 150 auxiliary officers."
Mr McGowan says WA's growing population means there is an urgent demand for more police resources.
"I have a traditional view of law and order," he said.
"I actually believe that you need to have police on the streets, in the suburbs and the towns, to deal with law and order and crime.
"I think the vast majority of the public of Western Australia agree with that sentiment."
The Police Union has described the Opposition's promise as a good start but says it wants more.
The union says it will not back away from its push for 800 new police over the same period.
Its president George Tilbury has called on the Premier to better Labor's offer.
"We're not saying that we will accept 500," he said.
"Five hundred is a good commitment, it's a start to the election campaign, and we seek a commitment from the other parties."
Mr Tilbury would not comment on whether the union's demands were an attempt to start a bidding war.
"We're not going to get into whether or not it is a bidding war but we seek from the Premier, on behalf of the Liberals and the Nationals, to make a commitment that meets or exceeds the 500 already given by Labor," he said.