KARACHI, Pakistan, April 29 —The Pakistan radio said to night that Indian allegations that Pakistani forces had entered Indian territory and had fired on Indian nationals were “absolutely untrue and base less” and charged that India was sending more infiltrators into Pakistan.

The radio also reported that the Pakistani President, Gen. Agha Mohammad Yahya Khan, had received a message from the Soviet Premier, Aleksei N. Kosygin, but did not disclose its contents. It warned that Pakistan might retaliate if India did not improve her treatment of Mehdi Masud, the senior Pakistani representative in Calcutta.

The Pakistan radio's denial and countercharge on reported border incursions followed an Indian charge that Pakistani troops had invaded Indian territory this week and had killed at least five Indians.

Earlier Charge Recalled

With emphasis, the radio termed this untrue and recalled an earlier Pakistani charge that armed Indians had killed 300 Pakistanis in a border raid last year.

On the contrary, the Pakistani radio said, Indian infiltrators have been illegally entering Pakistani territory and engaging in subversive activities. The report added that some Indian infiltrators had either been caught or killed, and that this had been confirmed by confessions from Indian soldiers captured on Pakistani soil.

The radio said that the message from the Soviet Premier was in response to one sent by President Yahya Khan to the Soviet Government earlier this week.

In it, Pakistan is understood, to have reaffirmed her contention that the situation in East Pakistan is her internal affair.