Reacting swiftly to an urgent request from the Carter administration, the Australian government today launched a diplomatic blitz in Asis to apply pressure on Iran to release the 50 American hostages in Tehran.

Australian diplomats immediately went into action in two key countries that have so far been silent about the plight of the hostages -- Indonesia and Malaysia, both predominantly Moslem.

At the same time, however, it has become clear that Prime Minister Malcolm Fraser's government would be unlikely to agree to any American request to boycott trade with Iran. According to government sources here, no such request has been made by Washington, either formally or informally.

Australian officials refused to name any of the countries being targeted in the diplomatic campaign. But apart from the two prime targets, they are understood to include India, the Philippines and Sri Lanka.

The request for Australia to use its influence in the area on behalf of the United States came in two communications yesterday. One was a formal cable in which Washington asked Australia to help. The other was a personal letter from Secretary of State Cyrus Vance to Foreign Affairs Minister Andrew Peacock, an old friend, in which Vance thanked Peacock for his public calls for the release of the hostages and repeated the request for more direct help.

Indonesia and Malaysia are considered by diplomats in this region as being particularly significant in any concerted world effort to win the release of the hostages. Both contain large Moslem populations, with Indonesia having one of the world's largest concentrations.

Australia is closely connected to both countries, politically as well as geographically. Malaysia and Australia are members of the Commonwealth and Australia sent strong air force and army contingents to Malaysia in the late 1950s and early 1960s when the newly independent former British colony was under threat from Communist insurgents. Today, Malaysia is the only foreign country where Australia stations a military force -- a standby squardron of Mirage fighters.

Indonesia is the most populous nation in Australia's region and is a key member the Association of Southeast Asia Nations, which Australia supports and encourages.

There was no immediate information on how any of the countries reacted to the Australian initiative.

On the orders of Peacock, the Australian foreign affairs department also called in the charge d'affaires at the Iranian embassy in Canberra, Pari Mokhtari, for a diplomatikc lecture. It was the second time since the hostages were seized that the Iranian charge here has been summoned before the department to be told in blunt language that Australia objected strongly to the seizure.

Australia's swift acceptance of the role of being Washington's emissary in this area on the hostage question veiled a serious concern in the Australian government about a possible U.S. request for a trade boycott against Iran.

It is an open secret in Canberra that Australia would have grave difficulty in joining such a boycott. At a meeting of Fraser's conservative cabinet earlier this week, a deep split on the issue was apparent.

Australia's trade with Iran was soaring over $200 million a year until the revolution that overthrew the shah also interrupted trade.

But Australia is still likely to sell some $140 million worth of meat and wheat to Iran this year, making it one of Iran's major suppliers of food.