The envelopes pour in daily containing checks for $10 from teachers, $25 from federal retirees and $5,000 from political action committees. All are headed for what is expected to be the most expensive congressional race in Virginia this fall.

The contributions have enabled Republican Rep. Frank R. Wolf to be the first on television, running $17,000 worth of television advertisements, and they have shown that his Democratic challenger, Arlington County Board Member John G. Milliken, is one of the best fund-raisers the Democrats have placed against Wolf.

"It's a competitive race, and it's a very expensive district to run in," said Chris Bowman, a National Republican Congressional Committee official. Wolf will "have to spend at least $500,000 for TV, so his fund-raising is more crucial."

Given that budget, it is not surprising that Wolf, seeking his fourth two-year term in the 10th District, started his fund-raising last year. He picked up nearly $105,000 in 1985 and brought his campaign chest up to $479,679 on June 30, according to the latest federal campaign finance reports. Since then, Wolf has gone past the halfway mark in his goal of raising $1 million. Milliken has raised $312,573 of his projected $550,000 budget since January and expects to be outspent by the Republican. "I don't expect to match him and I don't intend to," Milliken said. "If I can match him in a competitive sense, that's all I need to do."

The Democrat plans to spend about $300,000 on TV ads but probably will not take to the airwaves until after the Maryland Democratic primary in early September.

The Democratic Congressional Campaign Committee has given Milliken $10,000, pegging his race as one the national party can win this year, a change in expectations from the 1984 race in which Wolf easily outdistanced John Flannery.

"People are becoming believers again in Virginia Democrats and their ability to win campaigns," said Mark Johnson, a spokesman for the Democratic committee. "It started with Chuck Robb and continued with Gerry Baliles and the rest of the ticket in 1985."

The money for the two campaigns has come mostly from individuals, with Wolf leading in the number of contributors as well as the total amount.

Wolf has donations from 3,500 individuals, such as the $100 sent by a Falls Church dog breeder. Milliken's campaign has received money from 1,900 individuals, including a $25 contribution from a McLean woman who runs a day care center.

But the single largest chunks of the two campaigns have come from political action committees, whose $10,000 contributions, the maximum allowed by federal law, provide the financial base for any campaign. PACs have given Wolf nearly $140,000 and Milliken about $82,000.

Most of Milliken's PAC money has come from labor unions, not an unexpected development for a Democrat. He has received $10,000 each from PACs for the Communications Workers of America, the Committee on Letter Carriers and the National Education Association. The National Abortion Rights Action League sent $7,500.

Smaller contributions have come from PACs for United Steelworkers of America ($1,000), the AFL-CIO ($2,000), the International Brotherhood of Electrical Workers ($2,000) and the American Federation of State, County and Municipal Employees ($2,500).

PAC gifts to Wolf's campaign include a $10,000 contribution from the Virginia Bankers Association, $5,000 from the Realtors PAC, $4,750 from the American Medical Association and $3,000 each from the Newport News Shipbuilding Tenneco Employees and the National Association of Home Builders.

Smaller PAC contributions have come from Mobil Corp. ($1,000), Honeywell Employees ($1,500), Associated General Contractors ($2,250), the American Dental Association ($1,000), Coors Employees ($1,000) and the Greater Washington Board of Trade ($1,500).

Lawyers have contributed more heavily to Milliken, a lawyer practicing in the District in the same firm as Walter Mondale, than they have to Wolf, who is also a lawyer. Milliken has received about $45,000 from lawyers, including almost $7,000 from his partners at Winston & Strawn, while lawyers have sent Wolf about $12,000.

Those in the real estate/development industry have been more generous to Wolf, sending him about $107,000 to roughly $18,000 for Milliken.

Milliken's contributions have included relatively small amounts from developers doing business in Arlington, such as the $1,000 sent by J.W. Kaempfer of the development firm of the same name and $1,000 each from Giuseppe Cecchi and his wife Mercedes.

Wolf's contributions include $9,250 from family members or business partners of John T. (Til) Hazel Jr., one of Fairfax County's most prominent developers and attorneys. He has received $6,000 from members of the Walter Urquhart development firm and $2,000 from builder Milton L. Drewer III.

E.C. Robins, board chairman of the financially troubled, Richmond-based A.H. Robins pharmaceutical firm, sent Wolf $200, while Walter T. Ridder of Great Falls, director of Knight-Ridder Newspapers, gave Milliken $500.

The candidates are finding ways to spend the money, although Wolf has outspent Milliken $282,000 to $54,000 since January.

Wolf's single largest expense is the nearly $72,000 paid to the DCM Group, the Arlington political consulting firm of Ed DeBolt, who has worked for Wolf and other major Virginia Republicans. The firm is responsible for Wolf's polling, direct-mail and TV ads, a brochure and posters at Metro stops.

Wolf did not want to comment on the finances. Milliken, buoyed by his fund-raising, said his contributions have "sent a very clear message that this is going to be a horse race and something to look at closely."