Armco Steel Corp., the nation's fifth largest producer, said yesterday that it would file no new dumping complaints against foreign steel makers as a sign of support for the administration's plan to help the domestic steel industry.

The heart of the administration's plan is an accelerated antidumping procedure that will decide within 60 to 90 days whether foreign steel is being sold below cost (dumped) in violation of U.S. trade laws.

The adminstration will devise a set of reference prices for imported steel - based on Japanese production costs - and an automatic, accelerated administration dumping investigation will be launched if steel is imported below the reference price. If dumping is found, levies can be assessed within 60 to 90 days rather than the 13 months or more if takes under normal procedures.

A Japanese mission arrived here yesterday and presented to U.S. officials the first elements of the production cost data for Japanese steel companies that the administration needs to construct those reference prices.

The delegation, headed by Y. Iwasaki of Japan's Ministry for International Trade and Investment, met with Robert Crandall, deputy director of the Council on Wage and Price Stability.

The council, which monitors inflation trends by the White House, has been delegated the task of determining a set of reference prices, although Crandall told reporters Tuesday that it was not yet clear how many prices would have to be developed.

The administration task force that forged the steel program had hoped that only 50 or 60 prices would have to be developed, but officials now say they will probably have to set reference prices for several hundred items.

In Tokyo, the head of the giant Nippon Steel Corp. said that even though the Carter plan, which was unveiled Tuesday, will lead to reduced Japanese steel sales in the United States, he supported the idea because it would help settle the trade problems that exist between the United States and Japan.

Eighiro Saito said this concern for trade problems promoted the Japanese steel industry to cooperating with the Carter administration and supplying cost data.

Armco chairman C. William Verity said that because the company is "impressed and pleased by this administration's determination to seek solutions for the many problems which face our steel industry," the company would not file antidumping complaints it has been working on.

Armco filed a complaint against British steel imports on Monday.

Anthony M. Solomon, the Treasury undersecretary who headed the task force that came up with the steel assistance package, said Tuesday that the administration could either run the accelerated dumping program (which involves continuous monitoring of steel imports) or the normal program, but could not do both.

He said he hoped the major steel companies would withdraw their complaints after they see how the administration program is working.

Steel companies say the key to the program is the reference prices. Unless they are set high enough, steel producers will be unlikely to cooperate with the government.

Other steel executives have voiced cautious support for the program, although U.S. Steel president David M. Roderick said he feared that a part of the program that establishes loan guarantees for companies that need to modernize could be the first step toward nationalization of "as a minimum place the federal government in a position to control segments of the market."

Inland Steel Co. chairman Frederick G. Jaicks said that the proposals, "if properly implemented, could prove to be of major significance to improving the industry's outlook for future modernization and employment stability."