Gerald R. Ford yesterday kept his promise to remain an activist President until he left office. On his last full day in the White House he proposed gasoline price decontrols to Congress, upgraded the discharges of some wounded Vietnam combat veterans, telephoned Soviet Communist Party leader Leonid I. Brezhnev and granted a pardon to a Japanese-American woman known to World War II servicemen as "Tokyo Rose."

Ford's administration also was able to announce that consumer prices fell below the 5 per cent growth rate he announced as a target last year. The figure was 4.8 per cent.

The gasoline price decontrol proposal was both the most anticipated and most controversial of the President's 11th-hour actions.

Ford has steadily called for price decontrols on all forms of petroleum products, and indicated while he was vacationing at Vail, Colo., last month that he would attempt to decontrol gasoline prices before he left office.

The President's decontrol plan automatically will become law unless either house of Congress vetoes the proposal within 15 days. Stiff resistance is expected from Democrats, especially in the House.

"I feel Jerry Ford is a lame-duck President, and anything that he sends us will be treated in the manner that legislation of a lame duck is treated," said House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.).

Opponents of the decontrol say it could raise prices of gasoline as much as 8 cents a gallon. But estimates of industry and the Ford administration say a price rise would be limited to 1 or 2 cents a gallon, chiefly on unleaded gasoline.

In his final actions as chief executive Ford stuck closely to positions he advocated throughout his presidency.

This was especially true in his refusal to grant amnesty to Vietnam war resisters as requested by Jane Hart, widow of the late Sen. Philip A. Hart (D-Mich.).

Instead, Ford opted for the most limited option presented to him other than taking no action at all. He modified his own clemency program by allowing former servicemen who were wounded or decorated for valor in Vietnam to apply for upgrading of less-than-honorable discharges.

Administration officials estimated that it would affect at most 700 veterans and perhaps as few as 500.

These few servicemen probably owe their upgraded discharges to Jane Hart. When the President called her Dec. 26, to express his condolences, she asked him to give amnesty to draft resisters in memory of her husband.

Yesterday, in a "Dear Jane" letter, the President issued what was essentially a defense of his own original limited amnesty program.

"I have carefully reviewed my clemency program which enabled individuals to earn clemency discharges and pardons and believe it is a program consistent with America's best tradition of compassion and forgiveness," Ford wrote.

"I know how firmly and deeply you and Phil and your children have felt about Vietnam amnesty, and I respect that feeling and belief," the letter said. "However, I also have a strong personal belief that earned clemency was the right approach to healing our country's Vietnam wounds and creating a mutual understanding among all those individuals and families who were personally involved in the Vietnam war, from those who felt they could not serve to those who lost a child, a husband or a father."

The letter was read to Hart by a Ford aide before it was publicly released. Later, Hart issued a statement expressing her disappointment in muted language.

"This is a step in the right direction but unhappily a small one," she said.

One person who had no reason to be disappointed by Ford yesterday was Iva Toguri D'Aquino, a 60-year-old Chicago clerk, who was convicted of treason in 1949 for a broadcast she made to U.S. troops on Japanese radio, where she was one of several women whom Americans called "Tokyo Rose." She served 6 1/2 years in prison.

The Washington Post reported Tuesday that Ford had decided to pardon D'Aduino after a review of her case revealed trial irregularities and a feeling by some of the jurors who convicted her that she was innocent.

Newly elected Sen. S. I. Hanakawa (R-Calif.) said yesterday he had urged Ford for months to grant the pardon. He praised the decision, saying that D'Aquino had "remained loyal to the United States despite the fact that the United States treated her unjustly."

In other actions yesterday the President made "personal farewell" calls to a number of world leaders. Press secretary Ron Nessen said that one of the calls was to Brezhnev, and declined to indentify the other officials.

Ford also awarded the National Security Medal to his national security adviser, Brent Scowcroft, and the National Intelligence Distinguished Service Medal to Scowcroft's deputy, William G. Hyland.