LONDON (AP) _ A 17-foot condom stood next to Nelson's Column on Trafalgar Square today. In Perth, Australia, 147 crosses were laid at a busy intersection.

Observances of World AIDS Day included whimsical demonstrations to promote condom use, protests demanding more resources to combat the disease and vigils to remember the thousands who have died.

In Bombay, which has India's highest concentration of people infected with the virus, movie stars marched on Monday night, exhorting people to ''have fun, but don't forget Nirodh (a popular condom brand name).''

The World Health Organization, the U.N. agency sponsoring World AIDS Day, says about 2 million people in Asia could die of AIDS by the year 2000.

India is particularly at risk due to widespread illiteracy, lack of proper health care and tainted blood banks, according to experts.

In Manila, about 200 activists, mostly women, handed out condoms as they marched through the city's unofficial red light district.

Taiwan's Health Department urged women to accept blood tests at public clinics to find out if they were carrying the HIV virus, which causes AIDS.

In Tokyo, baseball star Sadaharu Oh joined other celebrities handing out AIDS information packets at a rally in the Ginza shopping district.

Children marched through Bangkok as the city government and an AIDS prevention project launched a one-year ''Community Mobilization'' education program.

In Adelaide, Australia, an Aboriginal resource booklet was launched and a nighttime candlelight vigil was planned for the 82 South Australians who have died of AIDS.

In Portugal, 1984 Olympic Champion marathon runner Carlos Lopes was running in a mini-marathon in Torres Vedras with a group of young people who are HIV- positive.

In Britain, 1.5 million red ribbons were distributed for the day and more than 400 events were planned, including parties to promote safe sex and a demonstration outside the prime minister's office demanding the appointment of a minister for AIDS.

The giant condom replica at Trafalgar Square was to draw attention to condom use as the most effective way of stemming the AIDS epidemic in Africa and Asia, said the Marie Stopes International charity, which was soliciting money at the site to fund condom distribution in the Third World.

In Israel, a condom dispenser was installed for the day at Israel's parliament building as part of the public awareness program and radio stations broadcast details of where to get free AIDS tests.

In the United States, federal health officials marked World AIDS Day with a new program to help businesses educate employees about AIDS and keep those with the disease working as long as possible.