A second U.S. Roman Catholic priest has been ordered by his religious superiors to drop out of politics, it was learned yesterday.

The new order affects the Rev. Robert J. Cornell, a Norbertine priest and former congressman who has been running for a U.S. House seat in Wisconsin.

Bishop Aloysius J. Wycislo of the Catholic Diocese of Green Bay, Wis., was told to enforce the no-politics order yesterday by the the Most. Rev. Jean Jadot, the apostolic delegate and Pope John Paul II's representative in Washington.

Cornell is a Democrat who served two House terms before losing in 1978.He could not be reached for comment.

The order that Cornell drop his bid to be reelected to the House came hours after Rep. Robert Drinan (D-Mass.), a member of the Society of Jesus (Jesuits), announced that he would obey a Vatican order and would not seek reelection this year.

"It is with regret and pain that I accept the decision of the Holy See," the 59-year-old Drinan told a Boston press conference.

"I am proud and honored to be a priest and a Jesuit . . . As a person of faith, I must believe there is work for me to do which is somehow more important than the work I am required to leave," said Drinan.

The order directing Drinan to drop out of the race came from the Rev. Pedro Arrupe in Rome. Arrupe, the highest ranking Jesuit, said his order "reflects the expressed wish of His Holiness Pope John Paul II" who, according to many U.S. Catholic officials interviewed yesterday, does not want priests in politics.

Since entering the House in 1970, Drinan has built a solid liberal record -- pushing for federal abortion aid, school desegregation and a host of social service programs. His positions angered many conservative Catholics.

But Drinan's religious superior, the Rev. Edward M. O'Flaherty, insisted yesterday that Drinan was not being singled out by church leaders.

"It has been stressed to me that Vatican and Jesuit authorities in Rome with to underline the point that the principal reason for the order was the present pope's convictions about the proper role of priests," O'Flaherty said.

O'Flaherty had attempted, on Drinan's behalf, to appeal the order. But he said he was told by the Vatican April 27 that the pope does not want priests in politics and that "further appeals would not be accepted."

However, because the papal directive apparently has not been put in writing yet, there was confusion among clerics yesterday as to what it meant and whether it applies to nuns, since nuns are not usually regarded as being part of the Catholic clergy. Two nun-politicians reached by The Washington Post yesterday said they intended to stay in office.

"They're talking about clergy, and women religious have not been characterized as clergy," said Sister Carolyn Farrell, mayor of Dubuque, Iowa.

Farrell, whose order is the Sisters of Charity, said she was concerned about the effects of the papal policy in the Third World, where many Catholic priests have embraced the "Liberation Theology" in ministering to the needs of their mostly poor constituencies.

" the little bit of leadership that people are getting in those countries just happens to come from the priests there," Farrell said.

In Belmont, N.C., Sister Mary Barbara Sullivan, a city council member and member of the Sisters of Mercy, said she intends to remain on the council, where she's served for the last three years.

"To me, it's a political ministry," said Sullivan, a Democrat. She said she would step down "if the church tells me to do so." But she said she has not seen anything in writing and added, "we're not in the clergy."

Also left in doubt is the effect the papal order has, or will have, on priests who are high-ranking political appointees, such as Msgr. Geno C. Baroni, an assistant secretary in the Department of Housing and Urban Development.

Baroni, a longtime liberal activist, was quoted by The Associated Press yesterday as saying that he would have to know more about the order before he could say whether or not it affects him.