Marking the 10th anniversary of what they regard as the "tragic" 1973 Supreme Court decision legalizing abortion, thousands of men, women and children staged a blocks-long march yesterday from the White House to Capitol Hill, demonstrating in favor of "pro-life" legislation that would outlaw abortion.

Buffeted by a cold, blustery wind under a gray sky and vying for the attention of Washington that was, for the most part, gripped by football fever, the estimated 26,000 abortion opponents walked along Constitution Avenue in a march suffused with intense religious feelings.

This 10th annual "March for Life" began at the Ellipse where participants from around the country heard Dee Jepsen, White House special assistant for women's organizations, read a letter of support from President Reagan.

"We have waited two years for Congress to rectify the tragedy of Roe vs. Wade. The time for action is now. I assure you that in the 98th Congress I will support any appropriate legislative action that will restrict abortion," Reagan's letter said. In his regular weekend radio broadcast yesterday, Reagan reaffirmed his support for curbs on abortion.

On Friday Reagan endorsed legislation proposed by Rep. Henry Hyde (R-Ill.) that would increase restrictions on federal funds for abortion, and which states that Congress finds " that the life of each human being begins at conception." It also states that the Supreme Court "erred" in its controversial 1973 decision.

Reagan has come under fire from abortion opponents among the "New Right" for not doing enough to get Congress to reverse the Supreme Court decision and outlaw abortion on demand.

Five congressmen addressed the protesters as they gathered at the Ellipse. Rep. Mark D. Siljander (R-Mich.) urged the people to unify their fight against abortion in order to make it easier for Reagan to take action.

"I'm sure his heart is right. But he has said to the movement, 'We need more unity, and until there is more unity what can I do? You have to get your act together.' So my call today is for the need for unity . . . to eliminate the one block to the president being as bold as he can possibly be," Siljander said.

In his remarks, Rep. Hyde said the "sanctity of life ethic" must gain supremacy over the "quality of life ethic." Reps. Lindy Boggs, (D-La.), Robert Young (D-Mo.) and Chris Smith (R-N.J.) also addressed the group.

Among the marchers yesterday was Roman Catholic Archbishop of Washington James Hickey, who joined 7th and 8th graders from Our Lady Queen of Peace School in Southeast Washington.

"I think people are more and more realizing that life indeed does begin at conception; that this life is very precious and they also realize more that the 'quality of life' argument can lead us into the same kind of putting to death of the retarded, the elderly, the terminally ill, the terrible things we saw in Hitler's Germany," Hickey said, as he listened with the others to the premarch speeches. Thomas J. Welsh, Roman Catholic bishop of Arlington, led the opening prayer of the march.

Although she declined to provide an estimate of yesterday's crowd, Mary H. Finnerty, secretary-treasurer of "March for Life" said organizers were "very delighted" with the turnout. In seven previous years, the annual March for Life drew crowds larger than yesterday's U.S. Park Police estimate of 26,000. The peak turnout occurred in 1980, when an estimated 100,000 people marched.

Besides Virginia, Maryland and the District, abortion opponents traveled from New Jersey, New York, Vermont, Kentucky, Tennessee, Michigan, South Dakota, Massachusetts, and other states. Most were members of "right to life" groups or of churches. One of the New Jersey groups was "Hispanics For Life." Another was a group of 400 Catholics from Bergen County who carried a statue of Our Lady of Fatima and recited the rosary as they walked.

Many of the participants arrived in buses painted white and bearing the symbol of the "pro-life" movement--a red rose. Two delegations carried small wooden caskets with a rose on top.

Michael Hatcher, a 35-year-old high school teacher from Stafford, Va., accompaned 114 other people who came from St. William of York Church in that town. Hatcher said he felt compelled to come and participate in the march, the first he has ever been in, because he has two adopted children and "I thank God everyday that their biological mothers had the strength to go through with what they did and give them life."

At Capitol Hill many of the marchers visited the offices of their congressional delegations to lobby those members they could find on behalf of the Hyde legislation.

About 400 of the marchers attended a dinner last night at the Hyatt-Regency Hotel. Sen. Jesse Helms (D-N.C.) was present, a protest official said.