If you frequent the all-night Zayre's on Sudley Road in Manassas, you might have encountered Charles A. Agnew handing out his campaign literature during one of his 24-hour stints at the store.

Agnew, a 52-year-old Democrat who has never run for office, is waging an old-fashioned battle for the 50th District seat in the Virginia House of Delegates that has been held for six years by Republican Harry J. Parrish, 65.

Like many of this fall's political races in fast-growing Prince William County, the Parrish-Agnew contest will be influenced by voters new to the area. The district, made up of the cities of Manassas Park and Manassas and central sections of the county along the I-66 corridor extending to the Fauquier County line, tallied a population of about 54,000 in 1980 that has swelled to an estimated 80,000.

Agnew acknowledges that he has a name recognition problem, but he thinks traditional methods, such as 24-hour marathons handing out fliers at shopping malls and going door to door in neighborhoods, will be effective in reaching both the new people and those who have been around awhile.

Parrish, a retired Air Force colonel and a longtime owner of a Manassas fuel company, will be tough to beat. In addition to his incumbency, his political roots in the 50th District go back 36 years, when as a Democrat he won his first election to the Manassas Town Council. He remained on the council 12 years until he became mayor, a post he held for 18 years, during which the town became a city.

In 1979, Parrish switched parties. Two years later, he resigned as mayor, and ran successfully for the House of Delegates.

In 1981 he finished second in a six-way race for three House seats in what was then a countywide district. The following year, in a special election because of redistricting, he won against Democrat John E. Bonfadini. Parrish faced no opposition in 1983 and 1985.

Agnew calls Parrish a "genuinely decent person," and both candidates say they intend to keep their campaigns on the high road.

Voters will have a choice between styles and political points of view. While Parrish says his most important role in Richmond has been "looking after constituent affairs" and that he is proudest of legislation directly affecting the lives of his constituents, Agnew says he would set his sights on larger issues.

Now retired from the Department of Energy and working as a contract investigator for the Department of Defense, Agnew is a lifelong Democrat, "a partisan kind of guy," as he puts it.

If elected, Agnew says he will join the ranks of Democratic legislators faithful to Gov. Gerald L. Baliles' policies. A Baliles delegate at the 1985 state Democratic convention, Agnew says he thinks "Baliles has got the state moving again."

One of the issues Agnew is most passionate about is the 4.5 percent state sales tax on food, which he wants to see repealed.

"It is not fair that a low-income person spending $100 on food then has to pay $4.50 in tax. He could use that money to buy extra loaves of bread."

Other areas where he says he would assume an active role are services for the elderly, human rights and transportation.

Recently Agnew received the Virginia state AFL-CIO endorsement in the race, which pleases him.

"I'm a friend of labor," he said. "My father headed the machinists' union in Philadelphia when I was growing up." The endorsement means 2,000 volunteer hours for him from the organization, according to Agnew.

Although both candidates say it will not be a campaign issue, Parrish suffered a heart attack in the spring. Early this month he underwent medical tests, and Parrish says his doctors have pronounced him fit to run.

"I don't think there'll be any issues in the campaign, except I'm a Republican and he's a Democrat, and I've given long-term service to the district," Parrish said.

Parrish tied for 60th place in a survey on the effectiveness of the 100 members of the state House of Delegates. The ballots for the survey, conducted earlier this year by The Virginian-Pilot and The Ledger Star in Norfolk, were sent to 489 lawmakers, state and local officials, lobbyists and reporters.

He is a member of the House committees on Finance, Conservation and Natural Resources, and Militia and Police. "This is an important year coming up, with the budget needs for education, social programs, mental health, community development," he said.

Parrish supports the governor's transportation program and voted to raise transportation revenue through a half-percent increase in the state sales tax.

"When it takes 45 minutes to get from Manassas to I-66 in the morning, you know the number one issue to address here is transportation," he said.

Parrish says he favors a comprehensive approach to solving traffic problems, including a commuter rail service, more van pools and buses as well as more roads.

Parrish also supported legislation establishing a resource recovery unit (incinerater) to be run jointly by Prince William County, Loudoun, Manassas and Manassas Park. Now under study, the unit would generate electricity by burning trash from those jurisdictions.

Facing an opponent so entrenched in the district's politics, Agnew acknowledges that he will have an uphill struggle. "My opponent represents 'Old Manassas,' " said Agnew, and added that "Old Manassas" is fast being taken over by the new.

"Regardless of the outcome," he added philosophically, "I'm glad I'm making the race. I believe in the two-party system."