Jim Finch started out as a lineman on the high school team in Arlington, Tex., back when it was a small town and football there was king. All he knew about the local post office was that his scoutmaster ran it.

In the intervening 28 years, Finch has learned a few more things about post offices without losing his ability to block.

The man who becomes deputy postmaster general this week--second-in-command of a workforce of 670,000 and a fiscal 1983 budget of $25 billion--has spent a decade with one of the most frequently pummelled federal agencies. He's given as good as he's gotten, and then some.

Since joining the U.S. Postal Service in 1973--two years after the the old Post Office Department was reorganized into an independent agency that was supposed to be run like a business--Finch, 46, has learned to use a combination of legal and financial acumen to fend off congressional and regulatory opponents.

Finch served a stint as chief rate counsel and when the Postal Rate Commission, the tiny agency that regulates the USPS, had questions about proposed rate increases, he was the one who had to provide the answers--if not always respectfully. Later, when Congress considered making the postmaster general a presidential appointee again, Finch, then one of the USPS's legislative liaisons, lobbied successfully on the Hill against the move.

More recently, when the Postal Service pushed through rate increases that took the price of a first-class stamp from 15 to 20 cents in three years, Finch, as senior assistant postmaster general for finance, provided the economic forecasts to justify the decisions.

How does he develop those forecasts?

"You get data on which to make inflation assumptions, volume assumptions and assumptions about mail mix and weight, you check labor contracts to find out if you've got cost-of-living increases coming due, put all these things in together. Then pray a little."

Among the small cadre of lobbyists and lawyers who specialize in the arcane issues of the postal rate structure--which mailers should pay what proportion of USPS costs--Finch commands considerable, although sometimes rueful respect.

"He knows what he's talking about; he's a very effective advocate," said David Minton, who, as a congressional staff expert on postal issues, sparred with Finch at Capitol Hill hearings in the 1970s, and now, as a lobbyist for the Magazine Publishers Association, spars with him on rate issues.

Minton added that Finch and Postmaster General William F. Bolger have eased long-standing tensions between the Postal Service and its legislative overseers.

But a lobbyist who asked to remain anonymous said that Finch also helped exacerbate the hostility between USPS and the rate commission, which, although ultimately it can't block postal rate increases, can prolong the process through lengthy hearings and requests for justification. His dislike for the commission is well-known. One attorney characterized Finch's early attitude at rate hearings as "insolent indifference."

Finch himself will not answer directly when asked if the rate commission should be abolished.

"I think there has to be some type of mechanism . . . to oversee the development of postal rates . . . . There needs to be some kind of public participation in that process." He added that he is not sure "whether that has to be a full-blown regulatory process with the attendant costs in both time and money."

"He's saying 'Sink 'em,' " said a congressional staff member familiar with Finch's attitude toward the rate commission.

"He's slippery," said Kathleen Conkey, who recently wrote a report criticizing the Postal Service's performance in trying to achieve financial independence from the government while proposing to curtail some services.

"You really have to be up to snuff in dealing with him," one lobbyist said. "If you ask him a question that's a bad question, he will respond only to the exact words and not give you the information you really want."

But when it comes to arguing the Postal Service's case or extolling what he sees as its growing maturity as a viable, break-even business, Finch is anything but the coy, good old Texas boy he sometimes appears to be. He can fill the air with facts so thick and fast that only the agile avoid being overwhelmed.

Asked if the Postal Service is unfairly preempting private telecommunications firms by offering a service that delivers paper copies of electronic messages, Finch discussed the virtues of using modern technology to speed the mail. He noted that the Postal Service pioneered the use of airplanes to transport the mail "and we didn't try to take over the airlines, no more than we would consider trying to become a telecommunications carrier."

Asked about the arguments of people such as Federal Trade Commission Chairman James Miller III, who advocate more private competition for the Postal Service, he came back with a flurry of figures: everything from the volume of mail delivered annually (114 billion pieces) to the cost of rural mail delivery.

He sums it all up with a flourish: "If you want to have uniform, universal service there isn't a more efficient way to do it."