"It's not ideal, that has to be said," former Australian ambassador to Washington Kim Beazley told AM.
"But there are mitigating circumstances."
Analysts said it is not normal for an embassy to go longer than a few months without an ambassador.
The Lowy Institute's Aaron Connelly told AM:
"We haven't heard much out of Washington about who they're thinking about for this post, which is unusual for this time in a presidency."
It has been speculated the US military's top commander in the pacific Admiral Harry Harris has been lined up for the job.
He was due to retire at the end of the year, clearing the way for him to take up the post early in the new year.
But it appears there has been a setback to that plan because his presumed replacement Admiral Scott Swift retired this week after learning he would not be getting the job.
That means Admiral Harris may have to stay on longer than planned.
"I wouldn't think that this would delay things too much, but it obviously delays it a bit," Mr Beazley said.
"I would think that, from our point of view, hanging on for Harry Harris, we ought to, even if it's the middle of next year."
With military tensions in Asia on the rise, Mr Beazley and other diplomatic veterans view Admiral Harris and his deep defence relationships in the region as highly valuable.
And Mr Beazley said the embassy's current Charge d'Affaires James Carouso is performing well in representing US interests in the interim.
Missing ambassador 'makes technically no difference'
Asked what difference it makes not having an ambassador in the embassy, Mr Beazley said: "In a technical sense, nothing at all."
"In the sense of a substantial American presence, something."
The ambassador vacancy in Canberra is not the only diplomatic post in the region that has not been filled.
There is still no word from US President Donald Trump's administration about who will fill two key regional appointments.
Assistant Secretary of State for South-East Asia-Pacific Affairs is the US State Department's top regional post, while the Assistant Defence Secretary for Asia-Pacific Security Affairs is the top Pentagon post for the region.
Pro-China former foreign minister Bob Carr said the vacancies show Mr Trump's administration is not focussed on this part of the world.
"It confirms that China is going to be bigger than the US as a force in South-East Asia," he told AM.
"Australians might bridle at that, because it's not the most comfortable thing for a country that is part of the British Empire and is now part of the US alliance system — but it is a fact of life."