Federal workers in Northern Virginia appear to be angry at President Reagan's economic policies and they may be venting their frustration on Republican Rep. Stanford E. Parris, according to a poll released yesterday.

The Associated Press/WRC-TV poll shows Democrat Herbert E. Harris II with an 8-point lead over Parris in the race for the 8th Congressional District seat. The poll of 276 likely voters gave Harris, the district's former congressman, a 48-to-40 percent lead with 9 percent undecided. Only 1 percent of the voters indicated they would support another candidate, suggesting virtually no support for Independent Austin W. Morrill Jr., the third candidate in the race.

Results of the poll, which was completed last week and has a 7-point margin of error, was greeted with cautious enthusiasm by Harris officials and disputed by those in the Parris camp. It shows Harris with a 23-point lead among households with one or more federal employes, a group that is a major voting bloc in the district. Fifty-six percent of the federal employe households polled said they supported Harris, while 33 percent favored Parris. Ten percent said they were undecided or did not plan to vote.

"I've been saying all along that this is a horse race, it's too close to call . . . ," Parris said yesterday. "Nobody ever said I was going to get elected by a landslide."

"If you're going to make a polling error, I like it this way," said Harris. "I think it's very close, but I think the shift among federal workers is very encouraging."

Both Harris and Parris, who have opposed each other for Congress twice before, released polls two weeks ago showing the race is a virtual tossup.

The AP poll, which was part of a statewide survey, shows the 53-year-old Parris with a 52-to-37 point edge with independent voters. It also shows that 79 percent of Democrats are supporting 56-year-old Harris while 65 percent of those who say they are Republicans are backing Parris.

Parris pollster Lance Tarrance of Houston said he questioned the AP telephone survey's validity because of its sample size, the margin of error, and the possible confusion of the candidates' names. Tarrance said his recent poll showed Parris holding about even among federal employe households.

"When you have a 7 percent plus or minus, the race could be dead even or it could have Harris 15 points ahead, which makes no sense," said Tarrance. "To have the Democrat that far ahead you would probably have to have a strong TV blitz or a major faux pas" by Parris, said Tarrance. He added that neither had occurred.

The new poll has a smaller percentage of undecided voters than the candidates' polls. "The more visible the contest, the lower the number of voters who are undecided," said a spokesman for NBC News in New York, which conducted the poll. "Both Harris and Parris are extraordinarily well-known because they've run against each other so many times."

The poll also showed that two-thirds of those who belong to federal employe households in Northern Virginia believe government workers, a major focus of Harris' campaign, are faring worse under the Reagan administration than in previous administrations.