The embattled Synthetic Fuels Corp. has agreed to delay $774 million in federal subsidies to three synfuels projects until President Reagan decides whether he wants the agency abolished, administration sources said yesterday.

The sources, speaking on condition of anonymity, said the pledge was made Wednesday by corporation Chairman Edward E. Noble during a meeting of the Cabinet Council on Domestic Policy.

Despite a 312-to-111 vote by the House in July to, in effect, scuttle the five-year-old, quasigovernmental corporation, its directors announced that by Sept. 13 they intended to approve subsidies for oil shale projects in Utah and Colorado and a heavy oil project in Texas.

That set off a flurry of letters to the White House from Capitol Hill, complaining that the corporation was thwarting the will of Congress, although the Senate has not acted.

Since the House vote, synfuels opponents and supporters have appealed to Reagan for help. So far, the only response has been a letter from a White House policy aide and comments from some Cabinet members reaffirming support for a compromise last year that cut the corporation's spending authority 40 percent, to $7.9 billion.

One administration source said the question of whether the president should support continuing, trimming or canceling the program was not decided at Wednesday's White House meeting.

"We'll bring that about for a decision hopefully the third week of September," the source said. "Until the larger question has been brought to the president, Chairman Noble agreed not to authorize any new contracts."

It was agreed "not to rush the process," another source said, adding, "It's a divided situation in the Cabinet."

Noble said in a telephone interview that it would be "totally improper" for him to comment on the meeting. But he repeated earlier assertions that "we're not trying to shove money out the door."

Other synfuels officials characterized the agency's plans as calling for an interim vote by the corporation's five directors at a meeting Tuesday on subsidies for the three projects, with a final vote Sept. 24.