President Reagan, impressed by the argument of Secretary of State Alexander M. Haig Jr. that now is not the time to make concessions to the Soviet Union, will keep the Russian grain embargo in place for the foreseeable future, according to White House sources.

The grain embargo was a significant issue in the 1980 presidential campaign.

Reagan assailed President Carter for imposing it in retaliation for the Soviet invasion of Afghanistan and said it was hurting American farmers far more than it was the Russians.

But this is not now the case, Reagan was told yesterday in a fullscale discussion of the issue during a Cabinet meeting.

The Soviets face severe grain shortages, he was told, and are using their hard currency to buy grain from Argentina and other countries. This was also one of the central arguments made in a recent report by the Heritage Foundation, a conservative, Washington-based research organization that recommened extending the embargo.

At his press conference last week, Reagan said he always thought the embargo, bitterly opposed by some Midwest farm organizations, was "more of a gesture than something real." He said that the only choice he had was to lift the embargo or broaden it.

Broadening it to include some technical products now being sent to the Soviets is still a possibility, according to one well-placed source. This source said that the president was "very impresseed" with Haig's argument that, at the very least, now is not the time to give the Soviets the concession they want most by lifting the embargo.

This is particularly true, the president has been told, in view of the signal he sent the Soviets in his news conference last week when he said that they are bent on world domination and consider it "moral" to lie, cheat and commit toward this end.

Any dealing with the Soviets, Reagan added, should take this into account.

The case for lifting the embargo was made in yesterday's Cabinet meeting by Secretary of Agricluture John Block, who argued that if the Soviets were going to be spending money abroad for grain they should be spending it in the United States. Meeting with reporters earlier in the week, Block described the embargo as "the most ridiculous thing I ever heard of."

Last week Block was successful in persuading Reagan to have the issue considered by the full Cabinet rather than just by the National Security Council. However, his argument at the Cabinet meeting appears to have been undercut by this year's reduced crops, for which most farmers appear to have adequate export markets. This in effect left a national security argument balanced against a campaign pledge.

The issue is highly sensitive for Reagan because of his repeated promises to lift the embargo if he were elected. But some of his aides argue privately that the situation has changed since he made the pledge, both because of the Soviet threats to Poland and because there has been some accumaulation of evidence that the embargo has made the Soviets pay out more of their limited hard currency, perhaps as much as $1 billion more, than they would have without the embargo.

Carter imposed the embargo on Jan. 4, 1980, with the support of most national farm organizations. His order blocked delivery of 17 million metric tons of wheat, corn and other products, most of it destined for livestock feed.

Carter's support from farm organizations declined along with farm income, which dropped by 22 percent in 1980. There is a dispute among agricultural economists about the embaro's role in this decline, with some placing more of the blame on the glut caused by 1979 bumper crops.

Even though farmers want the embargo lifted, there are some signs that this is a negotiable demand that could be traded for others. Marvin Meek, the president of the American Agriculture Movement, even while calling for a lifting of the embargo yesterday, said that it might be possible to go along with it if price supports are increased.

"It still boils down to what we said last November," the Associated Press quoted Meek as saying. "We're willing to go along with it as long as it doesn't destroy our markets."

However, there is no sign that price supports will be increased. On the contrary, an attempt may be made to lower them as part of the administration's effort to make substantial cuts in the federal budget.

Well aware of the sensitivity of the issue, the administration imposed a virtual gag order yesterday on White House press ssecretary James Brady, instructing him to say only that the embargo issue was still under discussion and that the president had not decided whether to retain or lift it.

Brady did as he was told, adding only that he expected the issue to come up at a future Cabinet meeting.

While declining to answer questions about the grain embargo at the daily White House briefing, Brady did provide the information that Reagan had implored his Cabinet yesterday to "go ye forth and seek minorities and women for your appointments."

Vice President Bush made a similar exhortation.

Organizations representing Hispanics, blacks and women have complained that insufficient numbers of their constituencies are getting jobs in the Reagan administration.