ZAGREB, Yugoslavia (AP) _ Margaret Thatcher, Britain's former prime minister, said on Croatian TV Friday that the West should recognize the independence of Croatia and Slovenia.

In an interview in London, she said the two secessionist Yugoslav republics should already have recognized because ''then we should have been in a position to supply them legally with arms with which they could defend themselves.''

She said the two republics deserved support in fighting ''communist Serbia, which has taken control both of the army and of the country.''

It was not just ''a civil war between two groups,'' Mrs. Thatcher said.

War broke out in Yugoslavia after Croatia and Slovenia separately declared independence June 25.

The army negotiated a withdrawal from Slovenia, but thousands of people have died in five months of fighting in Croatia.