President Reagan is planning a last-minute campaign stop in Northern Virginia despite the urgings of one of the region's two Republican congressman that he stay away.

Reagan's visit -- tentatively scheduled for the last week of October -- is primarily designed to boost the candidacy of GOP Senate candidate Paul S. Trible, who is locked in a tight race with Democrat Richard J. Davis.

But Rep. Stanford E. Parris, who is running an equally close race against Democrat Herbert E. Harris II, doesn't want Reagan in his district, fearing a presidential visit would be a drag on his candidacy, a Parris spokesman said. Other sources said that Parris had told White House aides he doesn't want Reagan to come to the district.

"I'm sure there are other places where the president would be more helpful," said Parris spokesman Dick Leggett.

A Reagan visit in the Washington suburbs would be particularly sensitive because of discontent over layoffs of federal workers and other policies affecting federal employes. Both Harris in the 8th district and Democrat Ira M. Lechner, who is running against Republican incumbent Frank R. Wolf in the 10th district, have sought to tap federal workers' anger with Reagan by linking their opponents to the president.

"I don't know the first thing about it," said Wolf campaign manager Tom Morr when asked about Reagan's plans. Morr declined further comment.

It is unclear how much Trible would welcome Reagan despite polls showing the president personally popular in Virginia. Earlier in the week, White House aides touted private campaign polls showing that Reagan visits during a recent nationwide campaign swing had boosted Republican candidates by five to ten points.

No such surge for Trible apparently materialized in Virginia after Reagan's visit Sept. 29. A previsit poll by a Richmond newspaper showed Trible ahead by four points. An Associated Press-WRC TV poll conducted last week had Trible two points behind.

Trible campaign manager Judy Peachee said today that private polling by the campaign indicated that Reagan's earlier visit "helped a little bit. Traditional Democrats went one way for Davis and the undecideds pulled out and went the other way [for Trible]," she said.