After a four-month hiatus, the Sandinista Army has resumed drafting young men, and Defense Minister Humberto Ortega said today that the draft would continue through this year as part of a mobilization against U.S.-backed rebels.

The announcement coincided with reports from residents of Chontales province, in the economically important cattle country in south-central Nicaragua, of the heaviest fighting they have experienced in 3 1/2 years of war. This move by the rebels of the Nicaraguan Democratic Force is in a relatively new area for them.

Defense Minister Ortega, who spoke on Army Day here, minimized the importance of the rebel penetration, insisting that it was nothing more than a "diversionary" tactic to draw Sandinista troops away from other areas.

"They are trying to decompress the tension that we have put on them in the north," said Ortega. The five northern provinces of Nicaragua have been the principal operation area for the rebels, or contras, as they are known here.

Journalists who visited Chontales province last week saw soldiers firing Soviet-made, multibarreled BM21 rocket launchers -- called Stalin's organs -- and saw special Sandinista counterinsurgency battalions operating. Ortega acknowledged that use of artillery and also Soviet-made helicopters in the province recently.

The Army has reported numerous skirmishes with the contras in the Chontales region in recent weeks and also several rebel attacks on state farms and government-run cooperatives, which usually are protected by small local militia units and have been favorite targets of the rebels in the north.

Although some residents have been evacuated from rural zones, there has been no massive resettlement of families from isolated areas as occurred in the north. The contras often have been able to get food, information and, sometimes, recruits in such areas. Ortega said he saw no reason for such resettlement in the Chontales area now.

Ortega refused to say whether the young men being drafted would be used to increase the size of the Army or only to replace of draftees who are due to leave the service at the turn of the year.

Last week, the official Barricada newspaper carried pages of names of young men asked to report. It was the first time since April that such a call had been made. About 4,000 names appeared in the newspaper, all from the west coast of the country, where there has been no fighting.

Ortega said the four months since the draft was halted had been used to study problems with the military service system. Human rights officials and Catholic Church leaders have complained that Sandinista draft sweeps often have included boys under the draft age of 17. They have also complained that some draftees received insufficient training before going into combat and that the Army has been used for Marxist indoctrination.

Thousands of young men have fled the country rather than answer the draft call, and some of them have ended up in the contras' ranks. That opposition to the draft and the drain it was causing on the economy were believed to be reasons for a slowdown in the draft call.