Tanzanian troops rested near here today still 17 miles from their next objective-the city of Jinja, where remnants of ousted president Idi Amin's army still may control a strategic power dam on the Nile River.

So far the advancing Tanzanian force, whose mission is to open Uganda's economic lifeline to Kenya, has encountered no opposition since leaving a point 12 miles east of the Ugandan capital of Kampala Wednesday morning.

But a clerk named Patrick Ngirizibu, who said he escaped from Jinja last night by boat, said Uganda's second-largest city was occupied by as many as 500 to 600 Amin soldiers.

In any case, the long-expected drive to Jinja and the Kenyan border, 70 miles further east, appears to have slowed.

Tanzanian officers had predicted that they would secure that the Owen Falls power plant by this morning.

A reconnaissance lieutenant interviewed at forward Tanzanian positions at Kinoni, reported that pro-Amin troops still had two tanks and an armored personnel carrier at the western end of the Nile River bridge over the dam.

The dam on the shores of Lake Victoria supplies all Uganda's power-and 15 percent of neighboring Kenya's.

At the present rate of advance, the Tanzanians may not be in a position to test Jinja's defences before Sunday.

Conditions inside the city of 50,000 were described as tense, with residents staying inside their homes without water for the past four days for fear of coming across looting Amin soldiers. Food was also said to be in short supply.

The clerk said troops loyal to Amin patrolled Jinja on foot and in vehicles.

He said Jinja was rife with rumors that residents had "disappeared," meaning they were abducted by Amin's troops, and that "Soldiers come for money if they think you have any."

The clerk also reported that a helicopter often used by Amin had been seen flying over Jinja almost everyday and that its presence had prompted residents to think he was still in the area. There have been no reports that Amin had been seen since Sunday, however. Two Ugandan pilots have told the provisional government that they saw him take off then in his private plane with a Libyan crew at the controls.

If pro-Amin troops are in such numbers inside Jinja-and willing to fight-the Tanzanians may be facing their first real battle since February.

But a relaxed Tanzanian soldier at Kinoni, watching comrades pose for photographers beside machine guns and recoilless rifles, said, "things are easy now, not like before. They [the pro-Amin soldiers] are cowards, they are always running away."

Meanwhile, a second Tanzanian-led column was reported marching north of bombo, 20 miles north of Kampala on its way to Nalasongola site of an Israeli-built airfield 50 miles further north.

Earlier reports suggested that the northern column would eventually push all the way to Gulu in the north. There it would eventually link up with the now eastward -bound troops who are expected to push north and then west after securing the area near the Kenyan border. CAPTION: Map, no caption, By Dave Cook-The Washington Post