Tanzanian troops today entered downtown Kampala, according to resident and diplomats in the Ugandan capital.

Reached by telephone communication from here, they said Tanzanian troops were touring the city calling on the remaining Ugandan troops still there to surrender.

The radio station, post office and "all Kampala" was taken over by 9 a.m. today, according to a revolutionary identifying himself as Abdul Hassen, speaking from Radio Uganda. "It's liberation, it's liberation-the people are very happy."

Early reports indicated the Tanzanian-led assault met little final resistance.

The liberation will go to Jinga," Abdul Hassen said, alluding to a city 40 miles farther east where President Idi Amin and the remnants of his army may yet make a final stand.

Late last night the invading force had converged on Kampala from as many as a half dozen directions, leaving only the Jinga road open to allow Ugandan army stragglers an escape route.

Amin's whereabouts were not known today. But exile sources in Nairobi claimed their agents had spotted him in a five-car convoy headed toward Jinja in midafternoon on Tuesday.

Diplomatic sources in Kampala said they counted more than 300 shells in the first 90 minutes of Tuesday's artilery and rocket barrage, slamming into downtown Nakasero areas as well as the upper class Kololo residential district and Makerere University in the northwest. Thereafter shelling reportedly was sporadic.

By nightfall, usually reliable sources placed Tanzanian infantry columns anywhere from five to seven miles from the city center along all approaches except the Jinja Road, purposely left open to allow the Ugandan forces to retreat and thus avoid street fighting in the capital.

The Tanzanian decision to heavily shell central Kampala for the first time represented a significant change in strategy since even in recent days they had spared the capital all but sporadic rounds.

Reports of casualties and damage were sketchy.

A shell reportedly landed in a mission school and blew out many windows, but caused no casualties among students and nuns.

Also reported damaged were the 10 story Standard Bank building, the Mulago Hospital and Amin's temporary command post on Nakasero Hill.

Other rounds reportedly landed in a British doctor's garden and in a judge's home on Kololo Hill.

Residents reported parts of the city were without power or water. People who have not fled Kampala have complained for weeks of ever dwindling supplies of food and petroleum products.

All shops reportedly were closed.

Radio Uganda came on the air a quarter hour late Tuesday morning. It broadcast intermittently, but only music. Most unusually it omitted both news bulletins and commentary.

Incongruously, the music included such songs as "Mack the Knife," "Mrs. Robinson" and old favorites by Tennessee Ernie Ford.

In late afternoon, a professor at Makerere University told callers he had just shaken hands with Tanzanian infantry troops at the agricultural faculty's farm. He estimated that in normal times that was about 10 minutes' drive from the city center.

Barring unforeseen developments, the invading forces are expected to move into the city center Wednesday morning.

Whether or not they pursue the remnants of Amin's force remained to be seen. The Tanzanian-led invading force so far has shown no disposition to deal knock-out blows to a harried and retreating adversary. CAPTION: Map, no caption, By Richard Furno-The Washington Post