No matter how you look at the numbers, business travelers were hit hard in 1991 by the consolidation of the airline industry.

On the brighter side, the recession appears to be keeping a lid on the cost of hotels, rental cars and meals while on the road. That may not please the suppliers of those travel services, but it certainly is good news for the people who pay the bills.Two companies that do regular measurements of air fare and other travel costs - Runzheimer International Ltd. and American Express Co. - recently issued reports that clearly show just how much fares were affected by airline- industry changes.

Recent changes include the bankruptcy of Pan Am, the acquisition of Piedmont by USAir and Midway ceasing operations.

Runzheimer, a Northbrook, Ill., consulting company, reported that business-travel costs in the 1991 fourth quarter were up dramatically compared with the third quarter, and especially compared with the fourth quarter of 1990. All of the blame went to surging air fares.

Runzheimer said air fares in the 1991 fourth quarter were 15 percent higher than they were the quarter before. And looking at the last quarter of 1990 against the fourth quarter of 1991, the ticket prices shot up 20 percent.

In the meantime, prices for the other components of the index - lodging, meals and car-rental rates - changed relatively little, a clear reflection of lower demand because of the recession.

The hotel costs, for instance, increased less than 1 percent between the third quarter and the fourth, and were up just 6 percent from the fourth quarter of 1990 to the same 1991 period. Car-rental rates actually declined by 1 percent from the third quarter to the fourth, and increased only 2 percent over the 12 months, from the end of 1990 to the end of 1991.

Runzheimer makes its comparison by looking at round-trip discounted fares normally paid by business travelers between 20 heavily traveled city pairs, and by tracking changes in rental-car rates, restaurant prices and hotel-room rates in major cities.

American Express measures air fare changes by looking monthly at what a sampling of their business-travel clients are paying on 100 airline routes, as well as looking at prices for the lowest discount tickets and full-coach seats. The fares that the business travelers are paying usually have to be bought at least three days in advance and are good only for a limited number of seats on each flight.

On a nationwide basis, between the first of December and the first of January, the typical fare paid by a business traveler was up 2 percent, full coach fares were up 3 percent and the lowest discount fares dropped 8 percent, American Express found.

But compared with the first of January 1991, Amex found that the typical business traveler's fare was up a whopping 21 percent, while full-coach fares were up just 4 percent and discount prices were down significantly, by 15 percent.

Certain cities got hit worse by the higher business-traveler fares than others, the travel agency found.

For travelers between Philadelphia and seven other major cities, the typical one-way business-traveler fare was up 35 percent, from $263 to $354 between Jan. 1, 1991 and Jan. 1, 1992. But discount fares actually fell a lot - 20 percent - in the same period.

In Orlando, ticket price increases were even more astounding. Between Orlando and six other cities, the average business-travelers' one-way fare was up 111 percent, from $222 to $470 between the first of 1991 and Jan. 1, 1992. Vacationers got hit, too, with one-way fares to Orlando up 28 percent year- over-year, from $117 to $151.

Here are the increases in the typical one-way business-traveler fare for other major cities, comparing prices on Jan. 1, 1991 to Jan. 1, 1992:

* Atlanta, up 46 percent, from $289 to $421.

* Boston, up 27 percent, from $278 to $354.

* Chicago, up 12 percent, from $357 to $400.

* Dallas, up 28 percent, $361 to $462.

* Denver, up 8 percent, from $463 to $499.

* Houston, up 39 percent, from $248 to $344.

* Los Angeles, up 12 percent, from $396 to $444.

* New York and Newark, up 22 percent, $351 to $428.

* San Francisco, up 1 percent, from $447 to $451.