By Amie Ferris-Rotman

MOSCOW (Reuters) - Russian lawmakers, worried about a falling birth rate, passed a law on Friday that abortion advertisements must carry a health warning.

Russia has one of the world's highest abortion rates and cutting this could help it stem a demographic disaster that is looming as its population shrinks.

Under the new law approved by the lower house of parliament, 10 percent of the space used in abortion ads must carry a list of possible negative consequences for women, including infertility, RIA news agency reported.

According to the lower house's website, duma.gov.ru, 2007 saw 1.5 million abortions -- almost on a par with the number of children born that year.

"These ads make young girls believe they won't have any problems interrupting a pregnancy," RIA quoted parliamentarian Viktor Zvagelsky as saying of current advertisements.

He said the law was drawn up as "the situation with abortions in Russia was depressing."

Though the Soviet Union was the first country in the world to legalize abortion on request in 1920, dictator Josef Stalin outlawed it again, from 1936 until he died in 1954, to try to boost the birth rate.

The Communists later encouraged new births with prizes and money, but since they were ousted two decades ago Russia's population has steadily dropped. It shrunk by more than 12 million between 1992 and 2008, to around 143 million.

The United Nations predicts that by 2050 Russia's population will have dropped by almost a fifth from today to 116 million. It has said overcoming racism and taking in more migrants could help Russia boost its population.

Health experts say key factors in the decline are poor diet leading to heart disease, heavy drinking by men, an HIV/AIDS epidemic spurred by heroin abuse and a high number of violent deaths.

The bill is expected to pass the upper house and be signed into law by President Dmitry Medvedev without problem.

The country's increasingly powerful Orthodox church weighed heavily into the abortion issue a year ago, calling for tougher rules to reduce their number. Feminists argued this would hurt women's rights.