Clarke feels the two are dangerous because "Zaheer is a wonderful bowler with the new ball and can also reverse-swing the old one, while Harbhajan has had a lot of success against Australia." Clarke, who has scored 4,514 runs in 62 tests, said the two bowlers could hold the key during the two Tests and three one-day internationals.

"These two are probably India's best bowlers and we will have to come up with a plan to combat them," Clarke said.

Allrounder Shane Watson agreed with Clarke.

"It is hardest to face the ball when it swings," he said about left-armer Khan's ability to use the seam.

"As for Harbhajan, he is a brilliant exponent of spin bowling," added Watson.

Harbhajan has taken 79 wickets in 14 Tests against Australia, his most against any opponent, while Khan has collected 34 in 13 Tests.

Clarke said Australia was confident of beating India, whose top test ranking was not at stake.

"It is going to be a tough challenge. India is a strong team, but if we can play our best cricket, we can beat them," Clarke said.

India won the last series 2-0 of four home Tests in 2008.

The first Test begins in Mohali on Oct. 1, and the second in Bangalore from Oct. 9.

The one-dayers are in Kochi (Oct. 17), Vishakhapatnam (Oct. 20) and Goa (Oct. 24).