PRESIDENT Reagan urgently pressed the House Republicans yesterday to help him with the IMF bill. The president knows that this legislation is essential insurance for the preservation and protection of the economic recovery that is now under way here in the United States. But that crucial thought does not yet seem to have percolated through to all of the Republican congressmen. The bill is scheduled to come up again in the House today, and it would be a disaster if it were defeated. The outcome will depend on the support that Mr. Reagan gets from his own party.

The Democratic leadership supports the bill, but the party is as usual split. By one rough calculation, it will take about 100 Republican votes--that's three-fifths of them--to ensure passage. In the preliminary votes on the bill last week, it didn't get nearly that many. The president is anxious, and he has reason to be.

This bill would authorize the Treasury to lend an additional $8.4 billion to the International Monetary Fund to help it stabilize the world's network of money and trade. The immediate threat is the gigantic accumulation of debt in several countries, most of them Latin American, that are now staggering under the burden of high interest rates. The American loans to the IMF are being matched by loans from other countries; the IMF will match them again with further loans from commercial banks to help keep the debtor countries from being forced into bankruptcy. As long as the lines of credit are open, trade will flow. One of these countries, Mexico, is the United States' third-largest customer after Canada and Japan. To keep Mexico open for business is no more than American self- interest.

Some of the House Republicans have been against the IMF bill because they think it's foreign aid. Some have been against it because they think that it subsidizes the New York banks, or because they think it's inflationary. Some have been against it simply because they've always been against it. Those aren't very good reasons. To call the bill foreign aid or a bank subsidy is a misconception on more than the ordinary scale. Nor is it inflationary --although a major default might become drastically deflationary, in the manner of the 1930s.

Mexico's financial crisis last summer and the near-collapse of the peso have imposed on its people a severe drop in their standard of living. The IMF is now working to repair the damage. Even those congressmen who have little interest in Mexico might keep it in mind that last year, in the midst of their enormous troubles, the Mexicans bought $12 billion worth of American exports. That represents several hundred thousand American jobs. Mr. Reagan fully understands that logic. How many of his party will stand with him?