The difference between the cost of operating the current Amtrak system and original proposals of the Carter administration also was incorrect in yesterday's Business & Finance section because of a typographical error. The correct figure is $166 million.

Faced with a continued rush by Americans to find passenger train seats and certain ambush on Capitol Hill for plans to reduce Amtrak's routes later this year, the Carter Administration retreated yesterday and endorsed more federal aid for the nationwide rail system.

After an early morning meeting with key congressional leaders, Secretary of Transportation Brock Adams endorsed House legislation that would add $65 million to Amtrak's operating funds for the next fiscal year and keep alive an unspecified number of trains now scheduled for abandonment on Oct. 1.

But there were indications last night that the administration's concession may have backfired. Some congressmen who had been supporting President Carter's plan for cutting Amtrak's routes by 43 percent - to eliminate $1.4 billion in operating deficits over the next five years - were reported to be angry over the change in policy, after they had been the subject of adverse newspaper editorials and other criticism for their support.

Congressional sources said there was growing support for a plan by Sen. Frank Church (D-Idaho) to simply freeze Amtrak's operations at the current level, with an authorization of $718 million for the fiscal year starting Oct. 1 - or $1.6 million more than the administration had supported until yesterday.

Church introduced his amendment on Tuesday with 19 bipartisan sponsors from all regions of the country, ranging in political thought from Barry Goldwater (R-Ariz.) to George McGovern (D-S.D.). The Church plan would mandate a new Amtrak evaluation of the ridership boom, which began last fall but has mushroomed to record levels since gasoline shortages first started this spring.

Sen. Lowell Weicker (R-Conn.) also has proposed $100 million of additional capital funds for Amtrak, to order new equipment in the coming year. Church will support the Weicker plan, an aide said.

After the capitol Hill meeting yesterday, Secretary Adams told reporters: "We are going to let people vote by buying tickets. There are not going to be any political trains," a reference to action by some members of Congress to keep specific trains in their states.

Adams emphasized that the administration is firmly opposed to the drive to retain all of Amtrak's operations "because it wastes energy and an enormous amount of money . . . to preserve it as is would be like putting formaldehyde into a corpse."

The compromise position he staked out for the administration amounted to effective support for Amtrak legislation already approved by the House Commerce Committee. On top of $552 million to cover operating losses in the next fiscal year, proposed by DOT, the House bill adds $65 million to retain some trains that have demonstrated increased ridership and to keep several trains on current routes because of the cost and time necessary for proposed rerouting.

Specifically, under the legislation pushed by House Transportation Subcommittee Chairman James Florio (D-N.J.), a formula will be used to keep in business trains where ridership is up. Based on recent data, this means that the Montrealer between Washington and the Canadian center will be retained along with one Florida-New York train scheduled for abandonment, and possibly the Chicago-Loredo InterAmerican, Washington-New Orleans Cresent, Washington-Cincinnati Cardinal and others.

In addition, because of Amtrak data showing the costs involved in rerouting originally proposed by the administration, the following trains would be kept on their current routes: Chicago-San Francisco Zephyr, Washington- and New York-Chicago Broadway Limited, Chicago-Los Angeles Southwest Limited and the Boston/New York-Chicago Lakeshore Limited.

"We are going to give the additional money being made available to Amtrak and have the select the trains that meet the criteria," Florio said.

But a spokesman for the National Association of Railroad Passengers was not impressed by yesterday's administration shift. "It's political suicide . . . not enough to accommodate the real needs and stupid to cut back on service at a time when the public is demonstrating that it wants more," said NARP Executive Director Ross Capon.

The rail passenger lobbying group supports continuation of the current system and new spending to buy equipment that could handle soaring demand. Amtrak ridership jumped 20 percent in May compared with last year while ticket revenues were up nearly 28 percent to record levels.

Capon contended that the Carter administration "can't have it both ways" - arguing on one side, as Adams has done, that the current Amtrak boom is an unusual development that will evaporate as Americans return to cars and, on the other hand, warning that the energy crisis is a permanent situation.

"They should be encouraging people to use the trains," the NARP official added.