SYDNEY, AUSTRALIA -- Australia's treasurer has announced a ban on foreign purchases of urban residential land, saying it is ''not necessarily the kind of investment we want or need.''

''It is not adding to the stock of housing -- the stock is essentially finite, particularly in some parts,'' said Paul Keating. ''There is very little investment benefit for Australians and for the Australian economy by nonresidents building up the price of what is essentially a fixed stock of property.''

As of noon last Tuesday, approvals for foreign acquisitions of developed residential real estate were approved only if they were made by Australian citizens living abroad, prospective immigrants who have received approval to take up permanent residence in Australia, or foreign companies seeking accommodations for senior executives moving to Australia.

The move does not interfere with the relaxed foreign investment guidelines being applied to foreign purchases of real estate for development purposes or to the purchase of hotels, motels and other tourist facilities.

''If there are any upside benefits, I should imagine it would be in less upward pressure on prices to the general benefit of the whole Australian community,'' he said.

Keating said the reason for the government's action was the strong demand by nonresidents for housing in Australia, ''which I think is one of the factors which is pushing up prices of residential real estate in the cities at the moment.''

Industry sources estimate that foreign investors, especially from Japan, have pumped up to $180 million each month into urban real estate.

The previous foreign investment guidelines required voluntary notification of purchases valued at more than about $430,000. Keating said there was considerable evidence that the voluntary notification guidelines were being ignored.

''The decision to clamp down was based largely upon what we know from the {foreign investment} notifications that we have had and also general reporting of what's been happening in the real estate markets,'' he said.

Keating said the government will introduce legislation to amend the Foreign Takeovers Act, which will require the prior notification by foreign interests of proposals to acquire urban real estate.

The Foreign Investment Review Board said penalties under the act for failure to comply with its provisions will result in fines ranging up to about $36,000