Although the federal government spends $4 billion a year sending its employes on trips, it wasn't until recently that it began paying much attention to what it spends on travel.

Over the past four years the Transportation Office of the General Services Administration has shifted its focus from supervising the government's motor pool fleet to managing federal travel. Recent innovations include:

* A two-year pilot project in which commercial travel agents, instead of secretaries and other officials, make reservations for government travel, lodgings and conventions. The GSA estimates that it will save $8.3 million this year by using the agents.

* Contracts with commercial airlines that allow federal travelers to fly between 469 designated pairs of cities, saving an estimated $65 million this year off the average coach rate.

* A hotel-motel discount program that allows federal travelers to secure rooms at 2,800 locations in 960 cities at rates 50 percent below the standard rate and 30 percent below the corporate rate. The estimated savings for fiscal 1983 will top $15 million.

"When we first thought about doing this, we didn't think we could compete with the corporate clients travel agents have to deal with," Transportation Director Ivan Michael Schaeffer said. "But as it turns out, we're getting a much better deal than any corporation."

WHAT'S NEXT? . . . The latest innovation is a "conference location selection model"--a computer program that tells decision-makers the five cheapest places to hold a meeting when government employes from different parts of the country are involved.

"It will end up saving the federal government millions of dollars a year in travel and expense costs," Schaeffer said, explaining that the system takes into account the current per diem rate paid to a federal traveler away from home and the costs of various kinds of transportation available.

So far, about a half-dozen federal agencies have called the GSA to use the system, including the Social Security Administration, which wanted to bring together 59 officials from its State Disability Determination Services division. The computer said Chicago was the cheapest place to hold the meeing--at a cost of $34,655.87--and said St. Louis, Lansing, and Champaign-Urbana, Ill., would cost within $200 of that. It would have cost the agency another $13,627 to go to Seattle, its first choice.

"It's still the agency's decision entirely where they'll go," Schaeffer said. He added that the Office of Management and Budget told the GSA to make sure agencies understood that they didn't have to follow the computer's advice.

PAPER WORK REDUCTION . . . The GSA is trying to get a law changed so that it can scrap its time-consuming system of reviewing receipts for per diem reimbursements. Now, federal travelers are given between $50 and $75 per day, depending on the city, but they must submit lodging receipts and all other bills over $15 to get paid. If approved by the OMB and Congress, travelers would be able to get their reimbursements without having to submit the receipts.

"You could stay with your brother or sleep on a park bench, we don't care," Schaeffer said, because, according to General Accounting Office figures, the government could save $42 million a year by eliminating the audits.