Like crime in the streets, congressional assaults on presidential foreign policy prerogatives are now so commonplace that even those that take place in broad daylight can go largely unreported. Just the other day, on the same morning that a House foreign affairs subcommittee was making headlines mugging the administration on Central America, a sister subcommittee, almost unnoticed, was knocking the president's Mideast policy senseless.

It was an open-door hearing to "mark up" foreign aid appropriations. The hearing room was packed, with a sizable representation of the Israeli lobby on hand. A State Department official stood by, apparently on instructions not to get involved. And so at a time when President Reagan is ostensibly engaged in intense personal efforts to resuscitate his own peace initiative by promising a restraining hand on Israel and offering encouragement and reinforcement for Jordan's King Hussein (partly via Egypt's President Hosni Mubarak), the subcommittee:

* Went beyond the administration's proposals to bestow upon Israel an increase of $365 million in grants--increasing economic aid by $65 million and transferring some $300 million of military aid from the category of a loan to an outright gift.

* Took a small but symbolic $25 million bite out of PL480 food funds for Egypt.

* Pointed an admonishing finger at King Hussein by putting a hold on the sale of sophisticated military equipment to Jordan (including F16 jets promised personally to the king by Reagan) until Hussein publicly commits himself to the recognition of Israel and to "prompt entry" into the peace process put forward in the Reagan "initiative" of last September.

The subcommittee's markup is not necessarily the last word. But roughly 170 House members have signed a resolution endorsing the strings on Jordan. The new Congress, moreover, is thought to be measurably more sympathetic to Israel (with the addition of 26 Democrats to the House) than last year's lame-duck gathering, which also approved an increase in aid to Israel that the administration opposed. This time around, according to a reliable committee informant, "not one word" of restraint was received from the State Department.

So you can't entirely blame the subcommittee. A representative from State, Deputy Assistant Secretary Robert Pelletreau, was available; for the most part his silence gave consent. On one occasion, when Rep. Mervyn Dymally (D-Calif.) did raise the question of whether some sort of parity between grant aid to Egypt and Israel had not been established as U.S. policy, Pelletreau stated specifically that the Reagan adminstration accepts no "formal linkage or formal ratio . . . between Egypt and Israel, although there is some tendency out in the area to view the two programs together."

There is more than a "tendency," according to veterans of Camp David. Although such "linkage" was not part of the Camp David Accord, both U.S. and Egyptian officials believe a "relationship" was agreed to at the time as a negotiating incentive to Egypt.

Whatever the case, the political and psychological effect has not been lost upon the parties directly involved as word of the subcommittee's actions has circulated among diplomats here. The inevitable effect is to thoroughly scramble the signal that Ronald Reagan has been sending publicly and pri vately both before and after

King Hussein's recent decision to stay out of the peace talks in the absence of a wave-on from PLO Chairman Yasser Arafat.

Much has been made of the king's recalcitrance--not to say "lack of courage." For his part, he has made plain his need for some clear sign that in any negotiations over the future of the Israeli-occupied West Bank, the United States could exercise some moderating influence on Israel. A freeze on further Israeli settlements, now expanding at an almost furious pace, has been one of his tests.

And not without some reason: when the president announced his new peace plan last fall, he called for a halt to further settlements; they proceeded apace. Thanks to a revealing series of dispatches from Jordan by the Wall Street Journal's Karen Elliott House, we now know that the president was much more explicit in private. By her account, in a secret letter handed over at a meeting with Hussein in the White House last December, Reagan promised Hussein: "You will not be pressed to join negotiations on (West Bank) transition arrangements until there is a freeze on new Israeli settlement activity."

How the administration proposes to encourage such a freeze while silently consenting to still more aid to Israel--and a congressional strong arm on Hussein, as well--is beyond explanation. Either the president wants it both ways with Israel and the moderate Arabs, which won't work, or he doesn't know what his administration is doing. Neither explanation does much credit to his command of foreign policy.