Seven months before the U.S. House and Senate elections, incumbents in Maryland and Virginia are beating even their most prominent challengers in the first test of their campaigns -- raising money.

Sen. Paul Sarbanes (D-Md.), targeted for extinction by the National Conservative Political Action Committee (NCPAC), has raised more than $550,000. Rep. Michael Barnes (D-Md.), who has no announced opponents, has accumulated more than $75,000 in contributions. And in two Northern Virginia races expected to be tests of the Reagan administration's popularity, GOP members of Congress Frank Wolf and Stanford Parris have raised more than three times as much as their Democratic rivals.

The spending totals, disclosed in reports filed yesterday with the Federal Election Commission, were a testament to the power of incumbency.

"It's typical. That's why incumbents are so hard to beat," said Rich Galen, of the Republican Congressional Campaign Committee. "If a letter says 'Help me with my reelection,' be it from a Frank Wolf or a Mike Barnes, it's more likely to get a response than one from Joe Smith, saying, 'I want to be your congressman someday.' "

Nothing illustrates that better than the two Northern Virginia races.

In the 8th District, incumbent Parris has raised nearly $180,000 since January 1981, with about $65,000 in contributions this year, according to the latest FEC reports. His longstanding Democratic rival Herbert E. Harris II, who is trying to reclaim the seat he lost to Parris two years ago, has collected about $52,000 in contributions.

In the 10th District, Wolf has raised about $104,000 since January 1981 -- more than four times as much as his most visible rival, Arlington Democrat Ira Lechner, a lawyer and veteran campaigner who began raising funds this year.

While accepting huge infusions of cash from political action committees set up by business, labor, trade, professional and ideological groups, candidates and their staffs clearly would like to play down their reliance on such support.

A Parris aide noted that "only $7,150 of the $64,922 we collected this year came from PACs." Last year, however, Parris received more than $63,000 from PACs, according to FEC reports. The aide said many of those "shouldn't count" as contributions for the coming election because they were used to help retire a 1980 campaign debt.

Parris' Democratic opponent, Harris, received about $25,000 in PAC funds. In the neighboring 10th District, Wolf, the baby food lobbyist who rode into Congress with more than $215,000 in PAC contributions two years ago, had received about $43,000 from those groups since January 1981.

"In a perfect world, every candidate would prefer to receive all his money from individuals . . . but campaigns are too expensive," said the GOP's Galen. "Everybody has to take PAC money, so you hold your nose and you do it. Of course, it is perfectly legitimate."

Sarbanes, who has reaped national attention as a liberal symbol since his targeting by NCPAC, pulled in about $107,000 or 25 percent of his funds from PACs, which can donate up to $5,000 to a candidate while individuals are limited to $1,000.

One of Sarbanes' potential Republican opponents, Montgomery County businessman Dallas Merrell, has raised about $43,000, including $10,000 he has lent to the campaign, according to his FEC report. The other Republican candidate in the race, Prince George's County Executive Lawrence J. Hogan, did not make his FEC report available yesterday, but as of last December had raised about $40,000.

In Virginia, two major candidates are campaiging to succeed Independent Sen. Harry F. Byrd. Rep. Paul Trible, the Republican Tidewater congressman who had been lining up commitments for support since last year, has raised about $108,000, much of it from his congressional district. State Del. Owen Pickett, a little-known Democratic lawyer and accountant from Virginia Beach, has collected about $40,000 since his announcement to run last month. graphics /photo: Sen. Paul Sarbanes ...raised more than $550,000