The ambassador of Communist Poland, smiling as he entered St. Matthew's Cathedral yesterday evening, said that he was "very glad and very pleased" that the new pope of the Roman Catholic Church is a Pole.

Ambassador Romuald Spasowski was echoing the feelings of joy and surprise expressed by many of the worshippers who attended a special "Mass on the Election of the Pope."

It was the daily 5:30 p.m. mass at the cathedral, but the crowd was larger than normal as word spread of the election of Karil Cardinal Wojtyla as the 264th leader of the Roman Catholic Church. The ambassador stood and sat along with others, as the routine of the mass went on. 'Faith Is Not Easy to Come By'

The ambassador, who was escorted to a place of honor in the first pew of the church, listened along with Catholics scattered among the pews of the cathedral to the words of the homilist, Auxiliary Bishop of Washington Thomas Lyons, as he described Pope John Paul II.

"He is a man of faith," Lyons said," in a time when faith is not easy to come by.

"He is a man who in his own country and in his own diocese has been a man of faith . . . a man who has addressed the essential message of Christianity . . . He has had no opportunity to go down the side roads, but through faith has sought freedom from evil, sin and oppression . . . It is a time of great rejoicing for all of us."

Assisting the chief celebrant, Archbishop Jean Jadot, the apostalic delegate and official representative of the Vatican to his country, at yesterdays mass were concelebrants Bishop Thomas Kelly, general secretary of the National Conference of Catholic Bishops. Bishop Eugene A. Marino, auxiliary bishop of Washington, Bishop Lyons and parish priests from the Washington area.

Although the general reaction of most parishioners was the same when asked how they felt about the new pope, several went beyond the usual litany of surprise and happiness.

"Its good for the ones that really believe in it," said William Reardon, a 35-year-old member of the congregation. "You've got to remember though that he's not God, he's just another man." 'Good to Have a Father Again'

"It's great," said Bob Best, a 40-year-old economist. "Catholics view the pope as father and it's good to have a father again."

Asked to comment on the new pope's Polish origin, Best, who described himself as half-Italian, laughed and said "it doesn't bother me at all."

Marie Gamboa, a nurse of Spanish descent, spoke as tears welled in her eyes. "I feel happy, just very happy. I only learned two hours ago, you know."

A 31-year-old attorney, who declined to give her name said "I don't know anything about him. It will be interesting to see what happens with a non-Italian pope."