U.S. Ambassador Andrew Young and British Fortign Secretary David Owen will meet later this month in Malta with the two leaders of Rhodesian nationalist forces fighting to overthrow Prime Minister Ian Smith's white-minority government.

Joshua Nkomo and Robert Mugabe, joint leaders of the Patriotic Front forces fighting in Rhodesia, announced the meeting in Maputo, Mozambique, yesterday. The State Department said the four will discuss further attempts to implement the Anglo-American peace plan for Rhodesia, which unilarterally declared independence from Britain in 1965.

Nkomo and Mugabe have accepted the plan as a basis for negotiating a settlement of the Rhodesian issue, but there has been little progress on working out speciftic details since Young and Iwen presented it late last summer.

Since then Smith has launched talks with three black nationalist factions within Rhodesia to try to work out his own settlement, which would most likely exclude the Patriotic Front.

Smith is trying to work out a settlement directly with the "internal" factions, which have not been invited to the Malta meeting, involving retention of control over security forces. The U.S. British plan calls for the white-minority government to relinquish control of the military and turn over power to an interim British administration.

The guerrilla warfare carried on by the Patriotic Front continued to have an impact in Rhodesia, according to censored dispatches from the capital, Salisbury.

The government announced new regulations making any man between 16 and 50 subject to military duty if he has lived in the country for a minimum of six months.

The move was expected to boost the size of the 55,000-man military force to defend against guerrilla attacks which have increasingly hit civilian areas. So far this month 13 white civilians have been killed in such attacks.

The government also announced that it had begun an amnesty program for guerrillas in the Patriotic Front, saying that "if they return in peace, their lives will not be endangered."

A source said government aircraft have been dropping leaflets for some time in operational areas within the country, offering the amnesty to the 7,000 to 8,000 members of the Patriotic Front who are believed to have infiltrated Rhodesia through Mozambique and Zambia.