The Virginia General Assembly convened here today, but virtually all of the 100 members of the House of Delegates left the State Capitol somewhat uncertain what they will be doing for the next 60 days.

One member of the House knew and he wasn't telling.

He is John Warren Cooke, the courtly, diplomatic speaker of the House, a Democrat who possesses what one legislator calls "the unfettered right" to assign all 100 delegates to their committees. Here, as in Congress and most state legislatures, committees are crucial to the ebb and flow of legislation.

And herd, as in 38 other states, the House speaker is unchallenged in his power to make committee assignments. That makes the 62-year-old Cooke, a member of the House since 1942 and one of its most private members, one of the most powerful officials in the state.

Through his appointments, Cooke can both "initiate and block" key legislation, some legislators say. At the least, his powers enable him to "set the philosophy of a committee," said Del. J. Paul Council, a conservative Democrat from Southside Virginia.

Cooke denies using his appointment powers to further his own conservative views, saying the House would not allow him to do that. "I just don't think that could be done," he said the other day as he interrupted a flow of delegates who had come to his new office overlooking the Capitol in search of better committee assignments.

Even so, when Cooke made his last round of committee assignments two years ago, some legislators and lobbyists were saying wihtin munutes of his selection that he had effectively killed chances for House approval of either the Equal Rights Amendment or collective bargaining for public employees. Both proposals ultimately died. A weekly newspaper publisher on Virginia's rural Middle Peninsula. Cooke traditionallyu runs unopposed and rarely takes public stand son issues being debated in the House. He is generally presumed to be opposed to both the ERA and public employee bargaining.

Because both issues are likely to surface again this year, attention has again been focused on Cooke's appointments. Since the Nov. 8 elections, and in many cases before that, some legislators and their associates have been trickling in and out of Cooke's offices here in hopes of getting some hint as to how he will re-shape the House's 13 major committees after the election last fall of all 160 House members.

To date, they have learned nothing. Cooke's traditional practice of waiting until several days after the Assembly convenes to make his appointments recently prompted angry and rare public criticism of him at a Republican legislative caucus in Arlington. State Sen. Wiley F. Mitchell (R-Alexandria) charged then that there is "no damn reason why" Cooke waits so long after the elections to make the assignments.

If he would make the announcements earlier, the Assembly could begin work almost immediately, Mitchell and other Republicans agree. "The way he (Cooke) runs the show stands in the way of a lot of progress," said Lel. Ray R. Garland (R-Roanoke).

Tuesday, on the eve of the session, the Republicans agreed to forward to Cooke a trhree-page memo outlining their suggestions for speeding up the House operations. But, as Cooke's expected announcements neared, no member of the House appeared to be willing to publicly criticize him.

No one except Cooke even knows when the assignments will be announced. The speaker himself said yesterday his list is "getting pretty well firmed up" but he may not announce it until Friday or "more likely" on Monday.

Although Cooke has the power to change assignments of every House member, he traditionally does not reassign returning delegates to new committees unless they ask for changes. As a result of an unusual number of retirements and defeats of senior members on two of the House's most prestigious commttees - Appropriations adn Privileges and Elections - many of th House's returning 81 members have competed with its 18 newcomers for the desired committees.

Winning Cook's support for such assignments is one of the most delicate and difficult trasks legislators face in and difficult tasks legislators face in Richmond. In the past, legislators have been known to invoke the blessings of congressmen, committee chairman, senior legislators, lobbyists and anyone, who - as Del. Robison B. James (D-Henrico) put it - is "someone who knows someone."

The criteria Cooke uses in making assignments include geographic balance, seniority,partisanship, and a person's "qualifications."

In few regions will this year's appointments be a closely watched as those Cooke hands out to Northern Virginians. Typically Cook apportions two of the major committees' 20 seats to each congressional district and there are openings for Northern Virginians on Appropriations and Privileges and Elections.

Del. Dorothy A. McDiamid (D-Fairfax), the most senior member of the Northern Virginia delegation, is jockeying with others for an assignment to the Privilleges and Elections Committee. This committee considers the Equal Rights Amendment, a measure that which McDiarmid has long championed.