Virginia Democratic Senate nominee Edythe C. Harrison, struggling to give her low-budget campaign a higher profile, surprised Republican Sen. John W. Warner yesterday by announcing she would start showing up next week at his campaign appearances.

Harrison sprang the idea on Warner in her opening remarks at a Northern Virginia forum on civil service issues. She used the debate at Oakton High School to continue the aggressive attack she used during a 90-minute debate broadcast throughout the state from Richmond Friday night.

Harrison, a former legislator from Norfolk, also said Warner should return any campaign contributions he has received from political action committees of defense corporations that she says have overcharged taxpayers for routine goods and services.

She noted that Warner had suggested Friday night that persons responsible for illegal overcharges should be "put in jail."

"How can you accept PAC money from those you would jail?" Harrison asked.

The twin assault on Warner before a crowd of about 250 persons added spice to a one-hour debate over which candidate would do more to help retired and current civil service employes.

In contrast to his usually deferential responses to Harrison Friday night and during much of the debate today, Warner told reporters that Harrison could damage her own campaign with her new tactics, which he dismissed as "gimmicks."

Noting that Harrison is the first woman to run statewide with major party backing, Warner said, "I hope she does nothing that discredits this unique opportunity she has . . . this is really a sad note on her part."

Asked what he would do if Harrison keeps her promise to follow him around the state, Warner said, "It will be a fast-moving campaign. If we meet along the way, splendid."

During the debate, Warner initially appeared to reject Harrison's proposal that they campaign together, but then said, "if you are along the way, welcome."

It was unclear today just when Harrison, 50, would begin trailing Warner's campaign. Her aides said she would review Warner's schedule and check with host groups before attending any function. "She's not going to barge in," one aide said.

Harrison's proposal followed a statement by Warner in Friday's debate that incumbents have an edge over challengers in raising funds.

Harrison's managers acknowledged that the tactic is designed to overcome her difficulties in attracting attention in the state.

Both candidates must file campaign finance reports Monday. Warner is expected to top $2 million while Harrison may reach $400,000.

Warner declined to discuss the issue of PAC donations after the appearance today, but again said sternly that his votes are not influenced by PAC contributions.

"I'm not going to reply to it at this time," Warner said after the debate. Aides said they were not certain that Warner would address the issue before the Nov. 6 election.

During the debate, Warner, 57, noted that Harrison also has accepted PAC contributions. "None of the political action committees that have given to her campaign do I want to put in jail," Harrison responded.

Aides to Warner, who is completing his first term, dismissed Harrison's attacks and said they would backfire.

"She's counting on getting free media," said Peter Loomis, Warner's press secretary. "There's no mystery to it. It's just a stunt and a not very useful one."

During yesterday's debate, Warner stressed his experience and said he is one of among the few senators who regularly "get out and fight" for federal workers, a potentially strong political force in the Northern Virginia suburbs of Washington.