Rep. Paul S. Trible Jr. (R-Va.) was saved by the bell yesterday. Trible, the leading unannounced candidate for the Republican nomination for the U.S. Senate in Virginia next year, was scheduled to accompany Rep. Stanford E. Parris (R-Va.) to a fund-raiser for Parris in Richmond last night.

Trible had agreed to the trip long before there was any hint that Parris, his Northern Virginia colleague, might challenge Trible for the seat being vacated by independent Sen. Harry F. Byrd Jr.

But moments before the House colleagues were scheduled to leave Capitol Hill for National Airport, Trible walked up one flight of stairs in the Cannon House Office Building to Parris' office and announced that he could not go. As a member of the House Armed Services Committee, Trible said he wanted to be present to answer the bells announcing upcoming votes on the military aid bill.

"I'm sorry, Stan," Trible said straight-faced, "but I must carry out my congressional duties." Outside Parris' office, Trible, his eyes twinkling, said, "No one is more supportive than I am of Stan's campaign for reelection to the House."

Last night's $100-a-person cocktail party at the Downtown Club in Richmond had been planned a month ago by Virginia bankers to show their appreciation for Parris' service on the House Banking Committee. But since Parris' name came up last week as a possible challenger to Trible, the event took on what one guest called an alternative agenda.

George L. Yowell, president of the Dominion National Bank, called Parris "a candidate worth considering," but said it is early for commitments. Joseph A. (Jack) Jennings of United Virginia Bank said he wants to "see what might develop." And J. Clifford Miller Jr., a longtime Byrd supporter, said "Harry fooled us all" by announcing his retirement. Miller called Trible "an attractive young candidate," but said he believes the nomination is "not locked up."

Some Republicans boosting Parris say Trible, 34, is too young and immature. But a Trible supporter at the party, Dr. Louis Williams, a Richmond physician who has been active in past conservative coalitions, said Trible "has matured rapidly, and if he makes the race, he'll age quickly."

Many of the guests said it was too soon after last month's election to be thinking about the Senate nomination. And several noted that Trible had been working for more than a year to line up support.

Among those greeting Parris was Gov. John N. Dalton, who himself is under continuing pressure to run for the suddenly available Senate seat. Earlier yesterday, Dalton repeated that he plans to retire from elective office when his term expires next month, but when pressed by reporters, added, "I'm not set in concrete about anything."

At the Parris reception, Dalton said, "I'd feel very comfortable supporting Stan" for the Senate. He added that he has told Trible, "I'm not obligated to anyone" and is not likely to make a commitment before next summer's GOP convention.

Parris said he came home last night encouraged that he had broadened his base of support, but is still undecided about whether to forfeit his House seat for a run for the Senate.

"Most people said they would like me to think about it," Parris said, but the pragmatic politician added, "I wouldn't expect them to say much else-- it's like not wanting to tell a guy he has bad breath."